nnrpd External Authentication Support

    A fundamental part of the readers.conf(5)-based authorization mechanism
    is the interface to external authenticator and resolver programs.  This
    interface is documented below.

    INN ships with a number of such programs (all written in C, although any
    language can be used).  Code for them can be found in authprogs/ of the
    source tree; the authenticators are installed to *pathbin*/auth/passwd,
    and the resolvers are installed to *pathbin*/auth/resolv.

Reading Information from nnrpd

    When nnrpd spawns an external auth program, it passes information on
    standard input as a sequence of "key: value" lines.  Each line ends with
    CRLF, and a line consisting of only a dot followed by CRLF (".\r\n")
    indicates the end of the input.  The order of the fields is not
    significant.  Additional fields not mentioned below may be included;
    this should not be cause for alarm.

    (For robustness as well as ease of debugging, it is probably wise to
    accept line endings consisting only of LF, and to treat EOF as
    indicating the end of the input even if ".\r\n" has not been received.)

    Code which reads information in the format discussed below and parses it
    into convenient structures is available authenticators and resolvers
    written in C; see libauth(3) for details.  Use of the libauth library
    will make these programs substantially easier to write and more robust.

  For Authenticators

    When nnrpd calls an authenticator, the lines it passes are

        ClientAuthname: user\r\n
        ClientPassword: pass\r\n
        .\r\n

    where *user* and *pass* are the username and password provided by the
    client (e.g. using AUTHINFO).  In addition, nnrpd generally also passes,
    if available, the fields mentioned as intended for resolvers; in rare
    instances this data may be useful for authenticators.

  For Resolvers

    When nnrpd calls a resolver, the lines it passes are

        ClientHost: hostname\r\n
        ClientIP: IP-address\r\n
        ClientPort: port\r\n
        LocalIP: IP-address\r\n
        LocalPort: port\r\n
        .\r\n

    where *hostname* indicates a string representing the hostname if
    available, *IP-address* is a numeric IP address (dotted-quad for IPv4,
    equivalent for IPv6 if appropriate), and *port* is a numeric port
    number.  (The *LocalIP* and *LocalPort* parameters may be useful for
    determining which interface was used for the incoming connection.)

    If information is not available, nnrpd will omit the corresponding
    fields.  In particular, this applies to the unusual situation of nnrpd
    not being connected to a socket; TCP-related information is not
    available for standard input.

Returning Information to nnrpd

  Exit Status and Signals

    The external auth program must exit with a status of 0 to indicate
    success; any other exit status indicates failure.  (The non-zero exit
    value will be logged.)

    If the program dies due to catching a signal (for example, a
    segmentation fault occurs), this will be logged and treated as a
    failure.

  Returning a Username and Domain

    If the program succeeds, it must return a username string (optionally
    with a domain appended) by writing to standard output.  The line it
    should write is exactly

        User:username\r\n

    where *username* is the string that nnrpd should use in matching
    readers.conf access blocks.  The "User" parameter is case-insensitive.

    There should be no extra spaces in lines sent from the hook to nnrpd;
    "User:aidan" is read by nnrpd as a different username than "User:
    aidan".  If a domain is provided, it would for instance be
    "User:aidan@domain".

    Note that nnrpd implements a five-second timeout for the receipt of this
    line.

Error Messages

    As mentioned above, errors can be indicated by a non-zero exit value, or
    termination due to an unhandled signal; both cases are logged by nnrpd. 
    However, external auth programs may wish to log error messages
    separately.

    Although nnrpd will syslog() anything an external auth program writes to
    standard error, it is generally better to use the messages.h functions,
    such as warn() and die().

    Please use the ckpasswd.c program as an example for any authenticators
    you write, and ident.c as an example for any resolvers.

HISTORY

    Written by Aidan Cully for InterNetNews.  This documentation was
    rewritten in POD by Jeffrey M. Vinocur <jeff@litech.org>.

    $Id: external-auth.pod 8200 2008-11-30 13:31:30Z iulius $