emacs/doc/misc/auth.texi

\input texinfo                  @c -*-texinfo-*-

@include gnus-overrides.texi

@setfilename ../../info/auth
@settitle Emacs auth-source Library @value{VERSION}

@set VERSION 0.3

@copying
This file describes the Emacs auth-source library.

Copyright @copyright{} 2008-2011 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''
in the Emacs manual.

(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.''

This document is part of a collection distributed under the GNU Free
Documentation License.  If you want to distribute this document
separately from the collection, you can do so by adding a copy of the
license to the document, as described in section 6 of the license.
@end quotation
@end copying

@dircategory Emacs lisp libraries
@direntry
* Auth-source: (auth).          The Emacs auth-source library.
@end direntry

@titlepage
@ifset WEBHACKDEVEL
@title Emacs auth-source Library (DEVELOPMENT VERSION)
@end ifset
@ifclear WEBHACKDEVEL
@title Emacs auth-source Library
@end ifclear
@author by Ted Zlatanov
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top Emacs auth-source
This manual describes the Emacs auth-source library.

It is a way for multiple applications to share a single configuration
(in Emacs and in files) for user convenience.

@insertcopying

@menu
* Overview::                    Overview of the auth-source library.
* Help for users::              
* Secret Service API::          
* Help for developers::         
* GnuPG and EasyPG Assistant Configuration::  
* Index::                       
* Function Index::              
* Variable Index::              
@end menu
@end ifnottex

@node Overview
@chapter Overview

The auth-source library is simply a way for Emacs and Gnus, among
others, to answer the old burning question ``What are my user name and
password?''

(This is different from the old question about burning ``Where is the
fire extinguisher, please?''.)

The auth-source library supports more than just the user name or the
password (known as the secret).

Similarly, the auth-source library supports multiple storage backend,
currently either the classic ``netrc'' backend, examples of which you
can see later in this document, or the Secret Service API.  This is
done with EIEIO-based backends and you can write your own if you want.

@node Help for users
@chapter Help for users

``Netrc'' files are a de facto standard.  They look like this:
@example
machine @var{mymachine} login @var{myloginname} password @var{mypassword} port @var{myport}
@end example

The @code{machine} is the server (either a DNS name or an IP address).
It's known as @var{:host} in @code{auth-source-search} queries.  You
can also use @code{host}.

The @code{port} is the connection port or protocol.  It's known as
@var{:port} in @code{auth-source-search} queries.

The @code{user} is the user name.  It's known as @var{:user} in
@code{auth-source-search} queries.  You can also use @code{login} and
@code{account}.

Spaces are always OK as far as auth-source is concerned (but other
programs may not like them).  Just put the data in quotes, escaping
quotes as you'd expect with @code{\}.

All these are optional.  You could just say (but we don't recommend
it, we're just showing that it's possible)

@example
password @var{mypassword}
@end example

to use the same password everywhere.  Again, @emph{DO NOT DO THIS} or
you will be pwned as the kids say.

``Netrc'' files are usually called @code{.authinfo} or @code{.netrc};
nowadays @code{.authinfo} seems to be more popular and the auth-source
library encourages this confusion by accepting both, as you'll see
later.

If you have problems with the search, set @code{auth-source-debug} to
@code{'trivia} and see what host, port, and user the library is
checking in the @code{*Messages*} buffer.  Ditto for any other
problems, your first step is always to see what's being checked.  The
second step, of course, is to write a blog entry about it and wait for
the answer in the comments.

You can customize the variable @code{auth-sources}.  The following may
be needed if you are using an older version of Emacs or if the
auth-source library is not loaded for some other reason.

@lisp
(require 'auth-source)             ;; probably not necessary
(customize-variable 'auth-sources) ;; optional, do it once
@end lisp

@defvar auth-sources

The @code{auth-sources} variable tells the auth-source library where
your netrc files or Secret Service API collection items live for a
particular host and protocol.  While you can get fancy, the default
and simplest configuration is:

@lisp
;;; old default: required :host and :port, not needed anymore
(setq auth-sources '((:source "~/.authinfo.gpg" :host t :port t)))
;;; mostly equivalent (see below about fallbacks) but shorter:
(setq auth-sources '((:source "~/.authinfo.gpg")))
;;; even shorter and the @emph{default}:
(setq auth-sources '("~/.authinfo.gpg" "~/.authinfo" "~/.netrc"))
;;; use the Secrets API @var{Login} collection (@pxref{Secret Service API})
(setq auth-sources '("secrets:Login"))
@end lisp

By adding multiple entries to @code{auth-sources} with a particular
host or protocol, you can have specific netrc files for that host or
protocol.  Usually this is unnecessary but may make sense if you have
shared netrc files or some other unusual setup (90% of Emacs users
have unusual setups and the remaining 10% are @emph{really} unusual).

Here's a mixed example using two sources:

@lisp
(setq auth-sources '((:source (:secrets default) :host "myserver" :user "joe")
                     "~/.authinfo.gpg"))
@end lisp

@end defvar

If you don't customize @code{auth-sources}, you'll have to live with
the defaults: any host and any port are looked up in the netrc
file @code{~/.authinfo.gpg}, which is a GnuPG encrypted file
(@pxref{GnuPG and EasyPG Assistant Configuration}).  

If that fails, the unencrypted netrc files @code{~/.authinfo} and
@code{~/.netrc} will be used.

The typical netrc line example is without a port.

@example
machine YOURMACHINE login YOU password YOURPASSWORD
@end example

This will match any authentication port.  Simple, right?  But what if
there's a SMTP server on port 433 of that machine that needs a
different password from the IMAP server?

@example
machine YOURMACHINE login YOU password SMTPPASSWORD port 433
machine YOURMACHINE login YOU password GENERALPASSWORD
@end example

For url-auth authentication (HTTP/HTTPS), you need to put this in your
netrc file:

@example
machine yourmachine.com:80 port http login testuser password testpass
@end example

This will match any realm and authentication method (basic or digest)
over HTTP.  HTTPS is set up similarly.  If you want finer controls,
explore the url-auth source code and variables.

For Tramp authentication, use:

@example
machine yourmachine.com port scp login testuser password testpass
@end example

Note that the port denotes the Tramp connection method.  When you
don't use a port entry, you match any Tramp method, as explained
earlier.  Since Tramp has about 88 connection methods, this may be
necessary if you have an unusual (see earlier comment on those) setup.

@node Secret Service API
@chapter Secret Service API

TODO: how does it work generally, how does secrets.el work, some examples.

@node Help for developers
@chapter Help for developers

The auth-source library lets you control logging output easily.

@defvar auth-source-debug
Set this variable to 'trivia to see lots of output in *Messages*, or
set it to a function that behaves like @code{message} to do your own
logging.
@end defvar

The auth-source library only has a few functions for external use.

@defun auth-source-search SPEC

TODO: how to include docstring?

@end defun

Let's take a look at an example of using @code{auth-source-search}
from Gnus' @code{nnimap.el}.

@example
(defun nnimap-credentials (address ports)
  (let* ((auth-source-creation-prompts
          '((user  . "IMAP user at %h: ")
            (secret . "IMAP password for %u@@%h: ")))
         (found (nth 0 (auth-source-search :max 1
                                           :host address
                                           :port ports
                                           :require '(:user :secret)
                                           :create t))))
    (if found
        (list (plist-get found :user)
              (let ((secret (plist-get found :secret)))
                (if (functionp secret)
                    (funcall secret)
                  secret))
              (plist-get found :save-function))
      nil)))
@end example

This call requires the user and password (secret) to be in the
results.  It also requests that an entry be created if it doesn't
exist already.  While the created entry is being assembled, the shown
prompts will be used to interact with the user.  The caller can also
pass data in @code{auth-source-creation-defaults} to supply defaults
for any of the prompts.

Note that the password needs to be evaluated if it's a function.  It's
wrapped in a function to provide some security.

Later, after a successful login, @code{nnimal.el} calls the
@code{:save-function} like so:

@example
(when (functionp (nth 2 credentials))
   (funcall (nth 2 credentials)))
@end example

This will work whether the @code{:save-function} was provided or not.
@code{:save-function} will be provided only when a new entry was
created, so this effectively says ``after a successful login, save the
authentication information we just used, if it was newly created.''

After the first time it's called, the @code{:save-function} will not
run again (but it will log something if you have set
@code{auth-source-debug} to @code{'trivia}).  This is so it won't ask
the same question again, which is annoying.  This is so it won't ask
the same question again, which is annoying.  This is so it won't ask
the same question again, which is annoying.

So the responsibility of the API user that specified @code{:create t}
is to call the @code{:save-function} if it's provided.

@defun auth-source-delete SPEC

TODO: how to include docstring?

@end defun

@defun auth-source-forget SPEC

TODO: how to include docstring?

@end defun

@defun auth-source-forget+ SPEC

TODO: how to include docstring?

@end defun

@node GnuPG and EasyPG Assistant Configuration
@appendix GnuPG and EasyPG Assistant Configuration

If you don't customize @code{auth-sources}, the auth-source library
reads @code{~/.authinfo.gpg}, which is a GnuPG encrypted file.  Then
it will check @code{~/.authinfo} but it's not recommended to use such
an unencrypted file.

In Emacs 23 or later there is an option @code{auto-encryption-mode} to
automatically decrypt @code{*.gpg} files.  It is enabled by default.
If you are using earlier versions of Emacs, you will need:

@lisp
(require 'epa-file)
(epa-file-enable)
@end lisp

If you want your GnuPG passwords to be cached, set up @code{gpg-agent}
or EasyPG Assitant
(@pxref{Caching Passphrases, , Caching Passphrases, epa}).

To quick start, here are some questions:

@enumerate
@item
Do you use GnuPG version 2 instead of GnuPG version 1?
@item
Do you use symmetric encryption rather than public key encryption?
@item
Do you want to use gpg-agent?
@end enumerate

Here are configurations depending on your answers:

@multitable {111} {222} {333} {configuration configuration configuration}
@item @b{1} @tab @b{2} @tab @b{3} @tab Configuration
@item Yes @tab Yes @tab Yes @tab Set up gpg-agent.
@item Yes @tab Yes @tab No @tab You can't, without gpg-agent.
@item Yes @tab No @tab Yes @tab Set up gpg-agent.
@item Yes @tab No @tab No @tab You can't, without gpg-agent.
@item No @tab Yes @tab Yes @tab Set up elisp passphrase cache.
@item No @tab Yes @tab No @tab Set up elisp passphrase cache.
@item No @tab No @tab Yes @tab Set up gpg-agent.
@item No @tab No @tab No @tab You can't, without gpg-agent.
@end multitable

To set up gpg-agent, follow the instruction in GnuPG manual
(@pxref{Invoking GPG-AGENT, , Invoking GPG-AGENT, gnupg}).

To set up elisp passphrase cache, set
@code{epa-file-cache-passphrase-for-symmetric-encryption}.

@node Index
@chapter Index
@printindex cp

@node Function Index
@chapter Function Index
@printindex fn

@node Variable Index
@chapter Variable Index
@printindex vr

@bye

@c End: