src/auths/README

   1 AUTHS
   2
   3 The modules in this directory are in support of various authentication
   4 functions. Some of them, such as the base64 encoding/decoding and MD5
   5 computation, are just functions that might be used by several authentication
   6 mechanisms. Others are the SMTP AUTH mechanisms themselves, included in the
   7 final binary if the relevant AUTH_XXX value is set in Local/Makefile. The
   8 general functions are in separate modules so that they get included in the
   9 final binary only if they are actually called from somewhere.
  10
  11 GENERAL FUNCTIONS
  12
  13 The API for each of these functions is documented with the function's code.
  14
  15   auth_b64encode       encode in base 64
  16   auth_b64decode       decode from base 64
  17   auth_call_pam        do PAM authentication (if build with SUPPORT_PAM)
  18   auth_get_data        issue SMTP AUTH challenge and read response
  19   auth_xtextencode     encode as xtext
  20   auth_xtextdecode     decode from xtext
  21
  22 INTERFACE TO SMTP AUTHENTICATION MECHANISMS
  23
  24 These are general SSL mechanisms, adapted for use with SMTP. Each
  25 authentication mechanism has three functions, for initialization, server
  26 authentication, and client authentication.
  27
  28 INITIALIZATION
  29
  30 The initialization function is called when the configuration is read, and can
  31 check for incomplete or illegal settings. It has one argument, a pointer to the
  32 instance block for this configured mechanism. It must set the flags called
  33 "server" and "client" in the generic auth_instance block to indicate whether
  34 the server and/or client functions are available for this authenticator.
  35 Typically this depends on whether server or client configuration options have
  36 been set, but it is also possible to have an authenticator that has only one of
  37 the server or client functions.
  38
  39 SERVER AUTHENTICATION
  40
  41 The second function performs authentication as a server. It receives a pointer
  42 to the instance block, and its second argument is the remainder of the data
  43 from the AUTH command. The numeric variable maximum setting (expand_nmax) is
  44 set to zero, with $0 initialized as unset. The authenticator may set up numeric
  45 variables according to its (old) specification and $auth<n> variables the
  46 preferred ones nowadays; it should leave them set at the end so that they can
  47 be used for the expansion of the generic server_set_id option, which happens
  48 centrally.
  49
  50 This function has access to the SMTP input and output so that it can write
  51 intermediate responses and read more data if necessary. There is a packaged
  52 function in auth_get_data() which outputs a challenge and reads a response.
  53
  54 The yield of a server authentication check must be one of:
  55
  56   OK          success
  57   DEFER       couldn't complete the check
  58   FAIL        authentication failed
  59   CANCELLED   authentication forced to fail by "*" response to challenge,
  60                 or by certain forced string expansion failures
  61   BAD64       bad base64 data received
  62   UNEXPECTED  unexpected data received
  63
  64 In the case of DEFER, auth_defer_msg should point to an error message.
  65
  66 CLIENT AUTHENTICATION
  67
  68 The third function performs authentication as a client. It receives a pointer
  69 to the instance block, and four further arguments:
  70
  71   The smtp_inblock item for the connection to the remote host.
  72
  73   The normal command-reading timeout value.
  74
  75   A pointer to a buffer, to be used for receiving responses. It is done this
  76     way so that the buffer is available for logging etc. in the calling
  77     function in cases of error.
  78
  79   The size of the buffer.
  80
  81 The yield of a client authentication check must be one of:
  82
  83   OK          success
  84   FAIL_SEND   error after writing a command; errno is set
  85   FAIL        failed after reading a response;
  86               either errno is set (for timeouts, I/O failures) or
  87               the buffer contains the SMTP response line
  88   CANCELLED   the client cancelled authentication (often "fail" in expansion)
  89               the buffer may contain a message; if not, *buffer = 0
  90   ERROR       local problem (typically expansion error); message in buffer
  91
  92 To communicate with the remote host the client should call
  93 smtp_write_command(). If this yields FALSE, the authenticator should return
  94 FAIL. After a successful write, the response is received by a call to
  95 smtp_read_response(), which should use the buffer handed to the client function
  96 as an argument.
  97
  98 ****