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Code Editor : draft-newman-sasl-c-api-xx.txt

Network Working Group                                          C. Newman
Internet Draft: SASL C API                                      Innosoft
Document: draft-newman-sasl-c-api-01.txt                     A. Melnikov
                                                         MessagingDirect
                                                           February 2003
                                                   Expires in six months

Simple Authentication and Security Layer C API

Status of this memo

This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [RFC2026].

Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

Abstract

Almost every protocol needs authentication.  However, there does not
   exist an authentication mechanism suitable for all organizations, nor
   is it likely that a small fixed set of authentication mechanisms will
   remain suitable.  SASL [SASL] provides the on-the-wire framework for
   authentication (and a security layer) which separates the design of
   authentication mechanisms from the protocols in which they're used.

The SASL protocol model suggests a software architecture where
   application protocols call a generic API to authenticate which in
   turn calls a generic plug-in interface for extensible authentication
   modules.  This memo documents the API used in one implementation of
   this architecture in the hope that it will be useful to others.  An
   associated memo documenting the plug-in interface is forthcoming.

1.     Conventions Used in this Memo

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The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [KEYWORDS].

This assumes familiarity the SASL [SASL] specification.

1.1.   Concepts

The following concepts are necessary to understand this
   specification.

realm
     A realm is a name (usually a domain-style name) associated with a
     set of users on a server.  One realm may span multiple servers.
     Alternatively, a single server may have multiple realms.  Thus
     there may be multiple users with the username "chris" on the same
     server, each in a different realm.  Some authentication mechanisms
     have a special field for the realm (e.g., DIGEST-MD5).  For other
     mechanisms, a realm can be specified by the client by using the
     syntax "username@realm" in the username field.

service
     A service is a basic function provided by one or more protocols.
     The GSSAPI service name [GSSAPI] registry is available at:

<http://www.iana.org/numbers.html#G>

This registry is used by SASL and the SASL API. The service name
     may be used for service-specific passwords for advanced users, or
     advanced authentication mechanisms may restrict the services a
     given server may offer.

virtual domain
     When a single server has multiple realms and there is a DNS server
     entry for each realm pointing to the same server IP address, then
     those realms are "virtual domains".  Virtual domains are extremely
     popular with web hosting services and are becoming more popular
     with POP mail services.  The key to providing virtual domain sup-
     port is that the client informs the server of the domain it
     believes it is speaking to either through a special protocol ele-
     ment or by using a username of the form "user@realm".

2.     Overview of the SASL C API

The SASL API is initialized once at process startup. The
   sasl_server_init() and sasl_client_init() functions provide basic

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initialization.

When a network connection occurs where SASL will be used, a connec-
   tion-specific context is created for authentication with
   sasl_client_new() or sasl_server_new().  The API implementation must
   support multi-threaded servers and clients by creating the connection
   context in a thread-safe fashion permitting multiple contexts in a
   given process.  At this point, the caller may adjust security policy
   for the context, and the set of mechanisms which are enabled is
   determined by requirements from the configuration or by the caller.

The server end of the API may request a list of enabled authentica-
   tion mechanisms either in general or for a specific user.  The client
   may either select a single mechanism or request a list from the
   server (if the SASL profile for the protocol in question supports
   that) and pass the list to the API for automated mechanism selection
   by configured policy.

The SASL exchange begins with sasl_client_start() which determines if
   one of the desired mechanisms is available on the client and may gen-
   erate an initial client response.  The client then sends the appro-
   priate protocol message to initiate the SASL exchange that the server
   passes to sasl_server_start().

The SASL exchange continues with calls to sasl_client_step() and
   sasl_server_step(), until the server indicates completion or the
   client cancels the exchange.

The server queries the user name and user realm resulting from the
   exchange with the sasl_getprop() routine.

A connection context is released with sasl_dispose() and process ter-
   mination is indicated with sasl_done().

There are a number of utility functions and customization functions
   available in the API for additional services.

Note, that all functions described in this documen can be implemented
   as macroses, so an application using this API MUST NOT assume that
   they are functions.

An application or library trying to use SASL API described in this
   document must include "sasl.h" include file.

3.     Basic SASL API Routines

This section describes the types and functions likely to be used by
   every caller of the SASL API.

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3.1.   Basic SASL API Data Structures

The following datastructures are basic to the SASL API.

3.1.1. sasl_callback_t

The sasl_callback_t structure is used for the caller of the SASL API
   to provide services to both the core SASL API and SASL plug-ins via
   callbacks.  The most important callback is the "getopt" callback (see
   section 3.3.3) which is used to retrieve security policy option set-
   tings from the caller's preferences.

typedef struct sasl_callback {
       unsigned long id;
       int (*proc)();
       void *context;
   } sasl_callback_t;

id is the label for the callback (XXX IANA registry needed), proc is
   a function pointer whose exact type is determined by the id, and con-
   text is a context variable which will be passed to the callback (usu-
   ally as the first argument).  The last callback in the list of call-
   backs is indicated with an id of SASL_CB_LIST_END.

If proc is NULL, this means that the application doesn't want to
   specify a corresponding callback, but would provide the necessary
   data via interaction.  See also section 3.1.4.

3.1.2. sasl_secret_t

The sasl_secret_t structure is used to hold text or binary passwords
   for the client API.

typedef struct sasl_secret {
       unsigned long len;
       unsigned char data[1];
   } sasl_secret_t;

The len field holds the length of the password, while the data field
   holds the actual data.  The structure is variable sized: enough space
   must be reserved after the data field to hold the desired password.
   An additional that binary passwords are permitted to contain '\0'
   characters.

3.1.3. sasl_conn_t

The sasl_conn_t data type is an opaque data type which reflects the
   SASL context for a single server connection.  Only one SASL API call

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using a given sasl_conn_t as an argument may be active at a time.
   However, each sasl_conn_t is independent and thus the SASL API may be
   used in a true multi-processor multi-threaded environment.

3.1.4. sasl_interact_t

The sasl_interact_t structure is used by sasl_client_start and
   sasl_client_step to request certain information from the application,
   when the application did not provide corresponding callbacks. For
   example, an application may choose to present a single dialog to the
   user in order to collect all required information interactively.

typedef struct sasl_interact {
       unsigned long id;
       const char *challenge;
       const char *prompt;
       const char *defresult;
       const void *result;
       unsigned len;
   } sasl_interact_t;

The id field holds the value of the callback ID. The prompt field
   contains a string that should be presented to the user. If non-NULL,
   challenge is a NUL-terminated string that will allow the user to pre-
   sent a specific credential when prompted. This is different from the
   prompt in that the prompt is more like a label for a text box (for
   example "Response:" while challenge is a string that tells the user
   what specifically is required by the response (for example, an OTP
   challenge string). The defresult field contains a default value, if
   any. Upon return from sasl_client_* the "result" field points to the
   defresult. The client must present the information in the challenge
   and the prompt to the user and store the result and its length in the
   result and the len fields respectively.

For example, SASL_CB_PASS interaction may contain the following
   information:
    id - SASL_CB_PASS
    challenge - NULL
    prompt - "Password:"
    defresult - NULL (no default).

3.2.   Basic SASL API Client Routines

This section discusses the functions likely to be used by every
   client caller of the SASL API.

3.2.1. sasl_client_init function

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Arguments:
            sasl_callback_t *callbacks

Results:
            SASL_OK        -- Success
            SASL_NOMEM     -- Not enough memory
            SASL_BADVERS   -- Mechanism version mismatch
            SASL_BADPARAM  -- Error in config file

This function initializes the client routines for the SASL API.

The callbacks argument is the default list of callbacks (see sec-
      tion 3.1.1 for definition of sasl_callback_t structure) and SHOULD
      include the sasl_getopt_t callback (see section 3.3.3). The call-
      backs may be NULL.  On success, SASL_OK is returned, and on fail-
      ure a SASL C API error code such as the ones listed above is
      returned.  This function may be called a second time to change the
      default callbacks used for new connections, but the first call
      must be made in a single-threaded environment.  The data refer-
      enced by the sasl_callback_t structure must persist until
      sasl_done() is called.

3.2.2. sasl_client_new function

Arguments:
            const char *service,
            const char *server_name,
            const char *iplocalport,
            const char *ipremoteport,
            const sasl_callback_t *prompt_supp,
            unsigned int flags,
            sasl_conn_t **pconn

Results:
            SASL_OK        -- Success
            SASL_NOTINIT   -- SASL API not initialized
            SASL_NOMECH    -- No mechanisms available
            SASL_NOMEM     -- Not enough memory

This function creates a client connection context variable.  As
      long as each thread uses its own connection context, the SASL C
      API is thread-safe.

The service argument is an IANA registered GSSAPI service element
      as defined in section 1.1.  It MUST NOT be NULL.

The server_name is the host name or IP address of the server to
      which the client is connecting. NULL may be used for server_name,

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but may result in advanced mechanisms such as Kerberos being
      unavailable.

The iplocalport is the string with the client IPv4/IPv6 address,
      followed by ":" and than by port number. An IPv6 address must be
      enclosed in "[" and "]". NULL may be used for iplocalport, but may
      result in mechanisms requiring IP address being unavailable.

The ipremoteport is the string with the server IPv4/IPv6 address,
      followed by ":" and than by port number. An IPv6 address must be
      enclosed in "[" and "]". NULL may be used for ipremoteport, but
      may result in mechanisms requiring IP address being unavailable.

User input to the SASL C API may be provided in two ways: either
      by supplying callbacks (prompt_supp) to this function, or by using
      an interaction model with the sasl_client_start/sasl_client_step
      functions. Callbacks are more convenient to obtain information
      programmatically, such as pulling authentication information
      directly from a configuration file. Interactions are more conve-
      nient if one wants to get all the data in parallel, for example by
      displaying a single dialog box instead of a separate popup for
      authentication name, authorization, password, etc.

The prompt_supp is a list of supported user prompting callbacks
      discussed in the section 3.1.1. The prompt_supp argument MAY be
      NULL, which means that interactions (i.e. prompt_need parameter to
      sasl_client_start (see 3.2.3) and sasl_client_step (see 3.2.4))
      are used instead of callbacks. If prompt_supp is NULL, the
      prompt_need argument to sasl_client_start (see 3.2.3) and
      sasl_client_step (see 3.2.4) MUST NOT be NULL.

The flags argument represents client-supported security flags.
      The only values currently supported are SASL_SECURITY_LAYER to
      indicate the client supports the SASL security layer, or 0 to
      indicate it doesn't.

The pconn argument is set to point to the newly created connection
      context.  The sasl_conn_t type is opaque to the calling applica-
      tion.

3.2.3. sasl_client_start function

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Arguments:
            sasl_conn_t *conn,
            const char *mechlist,
            sasl_interact_t **prompt_need,
            const char **clientout,
            unsigned int *clientoutlen,
            const char **mech

Results:
            SASL_NOTINIT   -- SASL API not initialized
            SASL_BADPARAM  -- conn or mechlist is NULL
            SASL_NOMECH    -- No matching mechanisms available
            SASL_NOMEM     -- Not enough memory
            SASL_INTERACT  -- User interaction needed to continue
                              (see prompt_need description below)
            SASL_OK        -- Success

This selects an authentication mechanism to use and optionally
      generates an initial client response.

The conn argument is the connection context from sasl_client_new.

The mechlist argument is a '\0' terminated string containing one
      or more SASL mechanism names.  All characters in the string that
      are not permitted in a SASL mechanism name [SASL] are ignored
      except for the purposes of delimiting mechanism names (this per-
      mits passing direct results from many protocol capability lists
      unparsed).  Unknown mechanism names are ignored (although
      SASL_NOMECH is returned if no known mechanisms are found).  Mecha-
      nisms are tried in an implementation-dependent order. Implementa-
      tions SHOULD try to use the most secure mechanism possible, within
      the constraints specified by the application (e.g. SSF value).

For applications which support interactions, the prompt_need argu-
      ment should initially point to a NULL pointer. If the selected
      mechanism needs information from the user (for example, username
      or password), then prompt_need will be set to point to an array of
      sasl_interact_t structures (terminated by an entry with id equal
      to SASL_CB_LIST_END), and sasl_client_start will return
      SASL_INTERACT.  After that the client must fill in the requested
      information and call this function again with the same parameters.

Applications that do not support interactions MUST pass NULL for
      prompt_need.

The clientout and clientoutlen parameters are set to the initial
      client response, if any.  If a protocol's SASL profile uses base64
      encoding, this represents the data prior to the encoding (see

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sasl_encode64).  If a protocol's SASL profile doesn't include an
      optional initial client response, then these may be NULL and 0
      respectively. The memory used by clientout is interally managed by
      the SASL API and may be overwritten on the next call to
      sasl_client_step or a call to sasl_dispose.

The mech argument is set to point to a '\0' terminated string
      specifying the mechanism actually selected using all uppercase
      letters.  It may be NULL if the client does not care which mecha-
      nism was selected from mechlist.

If sasl_client_start is called a second time using the same con-
      nection context, it will discard any cached information (e.g., the
      username and password) and restart the exchange from the begin-
      ning. <<???>>

3.2.4. sasl_client_step function

Arguments:
            sasl_conn_t *conn,
            const char *serverin,
            unsigned int serverinlen,
            sasl_interact_t **prompt_need,
            const char **clientout,
            unsigned int *clientoutlen

Results:
            SASL_NOTINIT     -- SASL API not initialized
            SASL_NOMECH      -- sasl_client_start not called
            SASL_BADPROT     -- server protocol incorrect/cancelled
            SASL_BADSERV     -- server failed mutual auth
            SASL_INTERACT    -- user interaction needed
            SASL_OK          -- success

This routine performs one step in an authentication sequence.

The conn argument must be a connection context created by
      sasl_client_new and used in a previous call to sasl_client_start.

The serverin and serverinlen parameters hold the SASL octet string
      received from the server.  Note that for those SASL profiles which
      base64 encode the exchange, this is the result after the removal
      of the base64 encoding (see the sasl_decode64 routine below). The
      serverin MUST have a terminating NUL character not counted by
      serverinlen

The prompt_need argument is the same as for sasl_client_start.

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The clientout and clientoutlen parameters hold the SASL octet
      string to encode (if necessary) and send to the server.

3.3.   Basic SASL API Callback Routines

This section describes the basic callback functions needed for a
      simple client implementation.  See the definition of sasl_call-
      back_t in section 3.1.1 for a description of the basic callback
      structure.

3.3.1. sasl_getsimple_t

Arguments:
            void *context,
            int id,
            const char **result,
            unsigned *len

Results:
            SASL_OK          -- success
            SASL_FAIL        -- error

This callback is used by the SASL API to request a simple constant
      string from the application.  This is used with id SASL_CB_USER
      for the username, SASL_CB_AUTHNAME for the authentication name (if
      different), and SASL_CB_LANGUAGE for a comma separated list of RFC
      1766 language tags.

The context is the context variable from the sasl_callback_t
      structure, the id is the id from the sasl_callback_t structure,
      and the callback is expected to set the result to a constant
      string and the len to the length of that string.  The result and
      len parameters are never NULL.

3.3.2. sasl_getsecret_t

Arguments:
            sasl_conn_t *conn,
            void *context,
            int id,
            sasl_secret_t **psecret

Results:
            SASL_OK          -- success
            SASL_FAIL        -- error

This callback is expected to create, prompt or locate a secret and
      set it in the connection context with sasl_setprop.  The conn

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argument is the connection context, the context and id parameters
      are from the sasl_callback_t structure. The id SASL_CB_PASS is
      used to request a clear text password.

3.3.3. sasl_getopt_t

Arguments:
            void *context,
            const char *plugin_name,
            const char *option,
            const char **result,
            unsigned int *len

Results:
            SASL_OK          -- success
            SASL_FAIL        -- error

This callback is used by the SASL API to read options from the
      application.  This allows a SASL configuration to be encapsulated
      in the caller's configuration system. Configuration items may be
      mechanism-specific and are arbitrary strings. If the application
      does not provide a sasl_getopt_t callback, then the API MAY obtain
      configuration information from other sources, for example from a
      config file.

The context is the context variable from the sasl_callback_t
      structure, the plugin_name is the name of plugin (or NULL), the
      option is the option name, and the callback is expected to set the
      result to a string valid till next call to sasl_getopt_t in the
      same thread and the len to the length of that string.  The result
      and len parameters are never NULL. If the name of plugin is NULL,
      a general SASL option is requested, otherwise a plugin specific
      version.

3.4.   Basic SASL C API Utility Routines

This section describes utility functions provided as part of the
      SASL API which may be used both by clients and servers.

3.4.1. sasl_decode64 function

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Arguments:
            const char *in,
            unsigned int inlen,
            char *out,
            unsigned int outmax,
            unsigned int *outlen

Results:
            SASL_BUFOVER    -- output buffer too small
            SASL_BADPROT    -- invalid base64 string
            SASL_OK         -- successful decode

This utility routine converts a base64 string of length inlen
      pointed by in into an octet string. It is useful for SASL profiles
      which use base64 such as the IMAP [IMAP4] and POP [POP-AUTH] pro-
      files.  The output is copied to the buffer specified by the out
      parameter.  It is NUL terminated and the length of the output is
      placed in the outlen parameter if outlen is non-NULL. The lenght
      doesn't include the terminating NUL character.

When the size of the output buffer, as specified by outmax, is too
      small, the function returns SASL_BUFOVER error code and the
      required length is stored in the outlen parameter if it is not
      NULL.

The function may also return SASL_BADPROT error code when it
      encounters an invalid base64 character.

3.4.2. sasl_encode64 function

Arguments:
            const char *in,
            unsigned int inlen,
            char *out,
            unsigned int outmax,
            unsigned int *outlen

Results:
            SASL_BUFOVER    -- output buffer too small
            SASL_OK         -- successful decode

This utility routine converts an octet string of length inlen
      pointed by in into a base64 string. It is useful for SASL profiles
      which use base64 such as the IMAP [IMAP4] and POP [POP-AUTH] pro-
      files.

The output is copied to the buffer specified by the out parameter.
      It is NUL terminated and the length of the output is placed in the

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outlen parameter if outlen is non-NULL. The lenght doesn't include
      the terminating NUL character.

3.4.3. sasl_errstring function

Arguments:
            int saslerr,
            const char *langlist,
            const char **outlang

Results:
            const char *

This converts a SASL error number into a constant string.  The
      second argument MAY be NULL for the default language, or a comma-
      separated list of RFC 1766 language tags.  The final parameter is
      set to the RFC 1766 language tag of the string returned which will
      be "i-default" if no matching language is found.  The strings are
      UTF-8.  This requires no context so it may be used for the result
      of an sasl_*_init or sasl_*_new result code.

3.4.4. sasl_errdetail function

Arguments:
            sasl_conn_t *conn

Results:
            const char *

This converts the last SASL error code that occured on a connec-
      tion to UTF8 string. It uses the SASL_CB_LANGUAGE callback (see
      section 3.3.1) to determine the language to use. It may return
      more detailed information than sasl_errstring does.

3.4.5. sasl_seterror function

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Arguments:
            sasl_conn_t *conn
            unsigned flags,
            const char *fmt,
             ...

Results:
            none

This function sets sets the error string which will be returned by
      sasl_errdetail.  It uses syslog()-style formatting (i.e. printf-
      style with %m as the string form of an errno error).

Messages should be sensitive to the current language setting. If
      there is no SASL_CB_LANGUAGE callback for the connection, text
      MUST be in US-ASCII.  Otherwise UTF-8 is used and use of RFC 2482
      for mixed-language text is encouraged.

<<This will also trigger a call to the SASL logging callback (if
      any) with a level of SASL_LOG_FAIL unless the SASL_NOLOG flag is
      set.>>

This function may be used by server callbacks.

If conn is NULL, the function does nothing.

3.4.6. sasl_erasebuffer function

Arguments:
            char *buf,
            unsigned len

Results:
            none

This function fills the buffer buf of the lenght len with '\0'
      characters.  The function may be used to clear from memory sensi-
      tive informations, like passwords.

3.5.   Basic SASL C API Server Routines

This section describes the basic routines for a server implementa-
      tion of a SASL profile.

3.5.1. sasl_server_init function

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Arguments:
            const sasl_callback_t *callbacks,
            const char *appname

Results:
            SASL_BADPARAM     -- error in config file
            SASL_NOMEM        -- out of memory
            SASL_BADVERS      -- Plug-in version mismatch
            SASL_OK           -- success

This function initializes the server routines for the SASL C API.

The callbacks argument is the default list of callbacks (see sec-
      tion 3.1.1 for definition of sasl_callback_t structure) and SHOULD
      include the sasl_getopt_t callback (see section 3.3.3). The call-
      backs may be NULL. The appname argument is the name of the calling
      application and may be used by server plug-ins for logging.  On
      success, SASL_OK is returned, and on failure a SASL C API error
      code is returned.  This function may be called a second time to
      change the default callbacks, but the first call must be made in a
      single-threaded environment. The data referenced by the
      sasl_callback_t structure must persist until sasl_done() is
      called.

appname specifies the application name. SASL API may use it, for
      example, for logging or to read an application specific configura-
      tion. A library must pass NULL as appname.  appname can be also be
      set with sasl_setprop function, and can be queried with sasl_get-
      prop. <<Specify option name here>>

3.5.2. sasl_server_new function

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Arguments:
            const char *service,
            const char *serverFQDN,
            const char *user_realm,
            const char *iplocalport,
            const char *ipremoteport,
            const sasl_callback_t *callbacks,
            unsigned int flags,
            sasl_conn_t **pconn

Results:
            SASL_OK        -- success
            SASL_NOTINIT   -- SASL API not initialized
            SASL_BADPARAM  -- Invalid parameter supplied
            SASL_NOMECH    -- No mechanisms available
            SASL_NOMEM     -- Not enough memory

This function creates a server connection context variable.  As
      long as each thread uses its own connection context, the SASL C
      API is thread-safe.

The service argument is an IANA registered GSSAPI service element
      as defined in section 1.1. It MUST NOT be NULL.

The serverFQDN is the fully qualified name of the server. It MUST
      NOT be NULL.

The user_realm specifies the default realm. A realm defines a set
      of users on the system for systems which support multiple user
      communities ("realms"). If user_realm is NULL, the value of
      serverFQDN is used as the default realm.

The iplocalport is the string with the server IPv4/IPv6 address,
      followed by ":" and than by port number. An IPv6 address must be
      enclosed in "[" and "]". NULL may be used for iplocalport, but may
      result in mechanisms requiring IP address being unavailable.

The ipremoteport is the string with the client IPv4/IPv6 address,
      followed by ":" and than by port number. An IPv6 address must be
      enclosed in "[" and "]". NULL may be used for ipremoteport, but
      may result in mechanisms requiring IP address being unavailable.

The callbacks argument is a set of server callbacks which may
      include a connection-specific sasl_getopt_t and/or an authoriza-
      tion routine.

The flags argument represents server-supported security flags. The
      only values currently supported are SASL_SECURITY_LAYER to

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indicate the server supports the SASL security layer, or 0 to
      indicate it doesn't.

The pconn argument is set to point to the newly created connection
      context.

3.5.3. sasl_server_start function

Arguments:
            sasl_conn_t *conn,
            const char *mech,
            const char *clientin,
            insigned int clientinlen,
            const char **serverout,
            unsigned int *serveroutlen

Results:
            SASL_CONTINUE  -- Another authentication step required
            SASL_OK        -- Authentication Complete
            SASL_NOTINIT   -- SASL API not initialized
            SASL_BADPARAM  -- Invalid parameter supplied
            SASL_BADPROT   -- Client protocol error
            SASL_NOMECH    -- Mechanism not supported
            SASL_NOVERIFY  -- User exists, but no verifier exists for
                              the mechanism
            SASL_TRANS     -- A password transition is needed to use mechanism

This begins an authentication exchange and is called after the
      client sends the initial authentication command.  The mech argu-
      ment is the mechanism name the client is requesting.  If the
      client includes an optional initial-response, it is passed in the
      clientin and clientinlen fields.  Otherwise NULL and 0 are passed
      for those arguments. The serverout and serveroutlen are filled in
      with the server response, if any.  If SASL_CONTINUE is returned,
      the server will need to wait for another client message and call
      sasl_server_step.  If SASL_OK is returned, the authentication is
      completed successfully, although server out data may be supplied.

3.5.4. sasl_server_step function

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Arguments:
            sasl_conn_t *conn,
            const char *clientin,
            insigned int clientinlen,
            const char **serverout,
            unsigned int *serveroutlen

Results:
            SASL_CONTINUE  -- Another authentication step required
            SASL_OK        -- Authentication Complete
            SASL_NOTINIT   -- SASL API not initialized
            SASL_NOMECH    -- sasl_server_start not called
            SASL_BADPARAM  -- Invalid parameter supplied
            SASL_BADPROT   -- Client protocol error
            SASL_NOVERIFY  -- User exists, but no verifier exists for
                              the mechanism
            SASL_TRANS     -- A password transition is needed to use mechanism

This routine performs one step in an authentication sequence.

The conn argument must be a connection context created by
      sasl_server_new and used in a previous call to sasl_server_start.

The clientin and clientinlen parameters hold the SASL octet string
      received from the client.  Note that for those SASL profiles which
      base64 encode the exchange, this is the result after the removal
      of the base64 encoding (see the sasl_decode64 routine). The cli-
      entin MUST have a terminating NUL character not counted by
      serverinlen.

The serverout and serveroutlen parameters hold the SASL octet
      string to encode (if necessary) and send to the client. If
      SASL_CONTINUE is returned, the server will need to wait for
      another client message and call sasl_server_step.  If SASL_OK is
      returned, the authentication is completed successfully, although
      server out data may be supplied.

3.6.   Common SASL API Routines

This section describes the routines that are common to both
      clients and servers.

3.6.1. sasl_listmech function

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Arguments:
            sasl_conn_t *conn,
            const char *user,
            const char *prefix,
            const char *sep,
            const char *suffix,
            char **result,
            unsigned int *plen,
            unsigned *pcount

Results:
            SASL_OK        -- Success
            SASL_NOMEM     -- Not enough memory
            SASL_NOMECH    -- No enabled mechanisms

This returns a list of enabled SASL mechanisms in a NUL-terminated
      string.  The list is constructed by placing the prefix string at
      the beginning, placing the sep string between any pair of mecha-
      nisms and placing the suffix string at the end.

When calling this function plen and pcount MAY be NULL.

This function returns the list of client side SASL mechanisms, if
      the conn was created by sasl_client_new and the list of server
      side mechanisms, if the conn was created by sasl_server_new. The
      list returned by this function must persist till a next call to
      sasl_free_listmech or sasl_listmech.

3.6.2. sasl_free_listmech function

Arguments:
            sasl_conn_t *conn,
            char **result

Results:
            none

This disposes of the result string returned by sasl_listmech.

3.6.3. sasl_setprop function

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Arguments:
            sasl_conn_t *conn,
            int propnum,
            const void *value

Results:
            SASL_OK          -- property set
            SASL_BADPARAM    -- invalid propnum or value
            SASL_NOMEM       -- not enough memory to perform operation

This sets a property in a connection context. Commonly used prop-
      erties with their descriptions are listed below:

SASL_SSF_EXTERNAL

Security layer strength factor (SSF) -- an unsigned integer usable
      by the caller to specify approximate security layer strength
      desired. It roughly corresponds to the effective key length for
      encryption, e.g.
       0   = no protection
       1   = integrity protection only >1   = key lenght of the cipher

SASL_SSF_EXTERNAL property denotes SSF of the external security
      layer (e.g.  provided by TLS). The value parameter points to
      sasl_ssf_t, that is described as follows:

typedef unsigned sasl_ssf_t;

SASL_SEC_PROPS

The value parameter for SASL_SEC_PROPS points to sasl_secu-
      rity_properties_t structure defined below. A particular implemen-
      tation may extend it with additional fields.

typedef struct sasl_security_properties
      {
          sasl_ssf_t min_ssf;
          sasl_ssf_t max_ssf;

unsigned maxbufsize;

/* bitfield for attacks to protect against */
          unsigned security_flags;
      } sasl_security_properties_t;

The min_ssf and the max_ssf define the minimal and the maximal

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acceptable SSF.

The maxbufsize specifies the biggest buffer size that the
      client/server is able to decode. 0 means that security layer is
      not supported.

The security_flags is a bitmask of the various security flags
      described below:

SASL_SEC_NOPLAINTEXT          -- don't permit mechanisms susceptible to simple
                                        passive attack (e.g., PLAIN, LOGIN)
       SASL_SEC_NOACTIVE             -- protection from active (non-dictionary) attacks
                                        during authentication exchange.
                                        Authenticates server.
       SASL_SEC_NODICTIONARY         -- don't permit mechanisms susceptible to passive
                                        dictionary attack
       SASL_SEC_FORWARD_SECRECY      -- require forward secrecy between sessions
                                        (breaking one won't help break next)
       SASL_SEC_NOANONYMOUS          -- don't permit mechanisms that allow anonymous login
       SASL_SEC_PASS_CREDENTIALS     -- require mechanisms which pass client
                                        credentials, and allow mechanisms which can pass
                                        credentials to do so
       SASL_SEC_MUTUAL_AUTH          -- require mechanisms which provide mutual
                                        authentication

SASL_AUTH_EXTERNAL

The value parameter for SASL_AUTH_EXTERNAL property points to the
      external authentication ID as provided by external authentication
      method, e.g. TLS, PPP or IPSec.

3.6.4. sasl_getprop function

Arguments:
            sasl_conn_t *conn,
            int propnum,
            const void **pvalue

Results:
            SASL_OK        -- Success
            SASL_NOTDONE   -- Authentication exchange must complete prior to
                              retrieving this attribute
            SASL_BADPARAM  -- bad property number

This requests a pointer to a constant property available through
      the SASL API.  The most common use by servers is to get the
      SASL_USERNAME property which returns the authorization identity
      (user to login as) from the SASL mechanism as a UTF-8 string in

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the pvalue parameter.  Additional properties are listed in section
      6.

3.6.5. sasl_dispose function

Arguments:
            sasl_conn_t **pconn

Results:
            none

This function disposes of the connection state created with
      sasl_client_new or sasl_server_new, and sets the pointer to NULL.
      If the pconn is already NULL the function does nothing.

3.6.6. sasl_done function

Arguments:
            none

Results:
            none

A SASL application that is finished with the SASL API must call
      this function.  This function frees any memory allocated by the
      SASL library or any other library state. After this call most of
      the SASL API function will again return the SASL_NOTINIT error
      code.

There must be a call to sasl_done for every successful call to
      sasl_server_init or sasl_client_init made. Only the final
      sasl_done does the actual cleanup; the preceding calls simply
      decrement an internal reference count.

Connection states MUST be disposed of with sasl_dispose before
      calling this function.

4.     SASL Security Layer Routines

This section describes the routines need to support a security
      layer.

4.1. sasl_encode function

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Arguments:
            sasl_conn_t *conn,
            const char *input,
            unsigned int inputlen,
            const char **output,
            unsigned int *outputlen

Results:
            SASL_OK        -- Success (returns input if no layer negotiated)
            SASL_NOTDONE   -- Security layer negotiation not finished
            SASL_BADPARAM  -- inputlen is greater than the SASL_MAXOUTBUF property

This function encodes a block of data for transmission using secu-
      rity layer (if any). The output and outputlen are filled in with
      the encoded data and its length respectively. If there is no secu-
      rity layer the input buffer is returned in the output. Otherwise,
      the output is only valid until a next call to sasl_encode or
      sasl_dispose.

4.1. sasl_decode function

Arguments:
            sasl_conn_t *conn,
            const char *input,
            unsigned int inputlen,
            const char **output,
            unsigned int *outputlen

Results:
            SASL_OK        -- Success (returns input if no layer negotiated)
            SASL_NOTDONE   -- Security layer negotiation not finished
            SASL_BADMAC    -- Bad message integrity check

This function decodes a block of data received using security
      layer (if any). The output and outputlen are filled in with the
      decoded data and its length respectively. If there is no security
      layer the input buffer is returned in the output. Otherwise, the
      output is only valid until a next call to sasl_decode or sasl_dis-
      pose.

5.     Advanced SASL API Routines

This section describes the less frequently used functions avail-
      able in the SASL API.

5.1.   Additional Initialization Routines

5.1.1. sasl_set_mutex function

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Arguments:
            sasl_mutex_alloc_t  *mutex_alloc,
            sasl_mutex_lock_t   *mutex_lock,
            sasl_mutex_unlock_t *mutex_unlock,
            sasl_mutex_free_t   *mutex_free

Results:
            None

The sasl_set_mutex call sets the callbacks which the SASL API and
      plug-ins will use whenever exclusive access to a process shared
      resource is needed.  A single-threaded client or server need not
      call this.  The types are designed to be compatible with the LDAP
      API [LDAP-API]:

typedef void *sasl_mutex_alloc_t(void);

On success, this returns a pointer to an allocated and initialized
      mutex structure.  On failure, it returns NULL.

typedef int sasl_mutex_lock_t(void *mutex);

This will block the current thread until it is possible to get an
      exclusive lock on a mutex allocated by the mutex_alloc callback.
      On success it returns 0, on failure due to deadlock or bad parame-
      ter, it returns -1.

typedef int sasl_mutex_unlock_t(void *mutex);

This releases a lock on a mutex allocated by the mutex_alloc call-
      back.  On success it returns 0, on failure due to an already
      unlocked mutex, or bad parameter, it returns -1.

typedef void sasl_mutex_free_t(void *mutex);

This disposes of a mutex allocated by mutex_alloc.

5.1.2. sasl_set_alloc function

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Arguments:
            sasl_malloc_t  *malloc,
            sasl_calloc_t  *calloc,
            sasl_realloc_t *realloc,
            sasl_free_t    *free

Results:
            None

This sets the memory allocation functions which the SASL API will
      use.  The SASL API will use its own routines (usually the standard
      C library) if these are not set.

typedef void *sasl_malloc_t(unsigned long mem_size);

This allocates memory mem_size bytes of memory.  The memory is not
      initialized to any particular value.  It returns NULL on a fail-
      ure, or when mem_size is 0.

typedef void *sasl_calloc_t(unsigned long elem_size,
                      unsigned long num_elem);

This allocates elem_size * num_elem bytes of memory.  The memory
      is initialized to 0.  It returns NULL on a failure or when either
      elem_size and/or num_elem is 0.

typedef void *sasl_realloc_t(void *mem_ptr, unsigned long
      new_size);

This changes the size of a memory block previously allocated by
      malloc or calloc, and returns a pointer to the new location (which
      may be different from mem_ptr).  If mem_ptr is NULL, it is identi-
      cal to the malloc function.

It returns NULL on a failure or when new_size is 0. On failure the
      original block is unchanged. When new_size is 0 the function works
      as the free function.

typedef void sasl_free_t(void *mem_ptr);

This releases the memory in mem_ptr that was allocated by the mal-
      loc or the calloc or resized by the realloc. If mem_ptr is NULL,
      the function does nothing and returns immediately. The contents of
      the memory may be altered by this call.

6.     Additional Properties

<<To be completed>>

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SASL_SSF          -- security layer security strength factor,
                           if 0, call to sasl_encode, sasl_decode unnecessary
      SASL_MAXOUTBUF    -- security layer max output buf unsigned
      SASL_DEFUSERREALM -- default realm passed to sasl_server_new or set with
                           sasl_setprop
      SASL_GETOPTCTX    -- context for getopt callback
      SASL_CALLBACK     -- current callback function list
      SASL_IPLOCALPORT  -- iplocalport string passed to sasl_server_new/
                           sasl_client_new
      SASL_IPREMOTEPORT -- ipremoteport string passed to sasl_server_new/
                           sasl_client_new
      SASL_SERVICE      -- service passed to sasl_*_new
      SASL_SERVERFQDN   -- serverFQDN passed to sasl_*_new
      SASL_AUTHSOURCE   -- name of the active plugin, if any
      SASL_MECHNAME     -- active SASL mechanism name, if any
      SASL_AUTHUSER     -- authentication/admin user (authorization id?)

7.     References

[IMAP4] Crispin, M., "Internet Message Access Protocol - Version
      4rev1", RFC 2060, University of Washington, December 1996.

[KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
      Requirement Levels", RFC 2119, Harvard University, March 1997.

[POP3] Myers, J., Rose, M., "Post Office Protocol - Version 3",
      RFC 1939, Carnegie Mellon, Dover Beach Consulting, Inc., May 1996.

[POP-AUTH] Myers, "POP3 AUTHentication command", RFC 1734,
      Carnegie Mellon, December 1994.

[SASL] Myers, "Simple Authentication and Security Layer (SASL)",
      RFC 2222, Netscape Communications, October 1997.

[GSSAPI]

8.    Acknowledgements

The editor would like to thank Rob Siemborski and Ken Murchison
      for providing useful feedback and suggestions.

9.    Author's and Editor's Addresses

Author:

Chris Newman
     Innosoft International, Inc.

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1050 Lakes Drive
     West Covina, CA 91790 USA

Email: chris.newman@innosoft.com

Editor:

Alexey Melnikov
     ACI WorldWide/MessagingDirect
     59 Clarendon Road
     Watford, Hertfordshire, WD17 1FQ, UK

Email: mel@messagingdirect.com

10.    Full Copyright Statement

This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this doc-
   ument itself may not be modified in any way, such as by removing the
   copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of develop-
   ing Internet standards in which case the procedures for copyrights
   defined in the Internet Standards process must be followed, or as
   required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER-
   CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
   Internet Society.

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A. Appendix A -- Design Goals

The design goals of the SASL C API are as follows:

o   To be simple and practical to use.

o   To provide related utility services in addition to core SASL func-
    tionality.

o   To be reasonably extensible.

o   To be suitable for use in a multi-threaded server or client.

o   To avoid dependancies on a specific memory allocation system, thread
    package or network model.

o   To be an independent service rather than a new layer.

B.     SASL API Index

<<To be completed>>

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${this.title}

Code Editor : draft-newman-sasl-c-api-xx.txt