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.

This file describes the Emacs auth-source library.

Copyright © 2008–2014 Free Software Foundation, Inc.

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”.

(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”

Overview Overview of the auth-source library.
Help for users
Secret Service API
Help for developers
GnuPG and EasyPG Assistant Configuration
GNU Free Documentation License The license for this documentation.
Index
Function Index
Variable Index

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1 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.

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2 Help for users

“Netrc” files are a de facto standard. They look like this:

     machine mymachine login myloginname password mypassword port myport

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

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

The user is the user name. It's known as :user in auth-source-search queries. You can also use login and 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 ‘\’.

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

     password mypassword

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

“Netrc” files are usually called .authinfo or .netrc; nowadays .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 auth-source-debug to 'trivia and see what host, port, and user the library is checking in the *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 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.

     (require 'auth-source)             ;; probably not necessary
     (customize-variable 'auth-sources) ;; optional, do it once
— Variable: auth-sources

The 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:

          ;;; 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 default:
          (setq auth-sources '("~/.authinfo.gpg" "~/.authinfo" "~/.netrc"))
          ;;; use the Secrets API Login collection
          ;;; (see Secret Service API)
          (setq auth-sources '("secrets:Login"))

By adding multiple entries to 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 really unusual).

Here's a mixed example using two sources:

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

If you don't customize auth-sources, you'll have to live with the defaults: the unencrypted netrc file ~/.authinfo will be used for any host and any port.

If that fails, any host and any port are looked up in the netrc file ~/.authinfo.gpg, which is a GnuPG encrypted file (see GnuPG and EasyPG Assistant Configuration).

Finally, the unencrypted netrc file ~/.netrc will be used for any host and any port.

The typical netrc line example is without a port.

     machine YOURMACHINE login YOU password YOURPASSWORD

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?

     machine YOURMACHINE login YOU password SMTPPASSWORD port 433
     machine YOURMACHINE login YOU password GENERALPASSWORD

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

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

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:

     machine yourmachine.com port scp login testuser password testpass

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.

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3 Secret Service API

The Secret Service API is a standard from freedesktop.org to securely store passwords and other confidential information. This API is implemented by system daemons such as the GNOME Keyring and the KDE Wallet (these are GNOME and KDE packages respectively and should be available on most modern GNU/Linux systems).

The auth-source library uses the secrets.el library to connect through the Secret Service API. You can also use that library in other packages, it's not exclusive to auth-source.

— Variable: secrets-enabled

After loading secrets.el, a non-nil value of this variable indicates the existence of a daemon providing the Secret Service API.

— Command: secrets-show-secrets

This command shows all collections, items, and their attributes.

The atomic objects managed by the Secret Service API are secret items, which contain things an application wishes to store securely, like a password. Secret items have a label (a name), the secret (which is the string we want, like a password), and a set of lookup attributes. The attributes can be used to search and retrieve a secret item at a later date.

Secret items are grouped in collections. A collection is sometimes called a ‘keyring’ or ‘wallet’ in GNOME Keyring and KDE Wallet but it's the same thing, a group of secrets. Collections are personal and protected so only the owner can open them.

The most common collection is called "login".

A collection can have an alias. The alias "default" is commonly used so the clients don't have to know the specific name of the collection they open. Other aliases are not supported yet. Since aliases are globally accessible, set the "default" alias only when you're sure it's appropriate.

— Function: secrets-list-collections

This function returns all the collection names as a list.

— Function: secrets-set-alias collection alias

Set alias as alias of collection labeled collection. Currently only the alias "default" is supported.

— Function: secrets-get-alias alias

Return the collection name alias is referencing to. Currently only the alias "default" is supported.

Collections can be created and deleted by the functions secrets-create-collection and secrets-delete-collection. Usually, this is not done from within Emacs. Do not delete standard collections such as "login".

The special collection "session" exists for the lifetime of the corresponding client session (in our case, Emacs's lifetime). It is created automatically when Emacs uses the Secret Service interface and it is deleted when Emacs is killed. Therefore, it can be used to store and retrieve secret items temporarily. The "session" collection is better than a persistent collection when the secret items should not live longer than Emacs. The session collection can be specified either by the string "session", or by nil, whenever a collection parameter is needed in the following functions.

— Function: secrets-list-items collection

Returns all the item labels of collection as a list.

— Function: secrets-create-item collection item password &rest attributes

This function creates a new item in collection with label item and password password. attributes are key-value pairs set for the created item. The keys are keyword symbols, starting with a colon. Example:

          ;;; The session "session", the label is "my item"
          ;;; and the secret (password) is "geheim"
          (secrets-create-item "session" "my item" "geheim"
           :method "sudo" :user "joe" :host "remote-host")
— Function: secrets-get-secret collection item

Return the secret of item labeled item in collection. If there is no such item, return nil.

— Function: secrets-delete-item collection item

This function deletes item item in collection.

The lookup attributes, which are specified during creation of a secret item, must be a key-value pair. Keys are keyword symbols, starting with a colon; values are strings. They can be retrieved from a given secret item and they can be used for searching of items.

— Function: secrets-get-attribute collection item attribute

Returns the value of key attribute of item labeled item in collection. If there is no such item, or the item doesn't own this key, the function returns nil.

— Function: secrets-get-attributes collection item

Return the lookup attributes of item labeled item in collection. If there is no such item, or the item has no attributes, it returns nil. Example:

          (secrets-get-attributes "session" "my item")
               ⇒ ((:user . "joe") (:host ."remote-host"))
— Function: secrets-search-items collection &rest attributes

Search for the items in collection with matching attributes. The attributes are key-value pairs, as used in secrets-create-item. Example:

          (secrets-search-items "session" :user "joe")
               ⇒ ("my item" "another item")

The auth-source library uses the secrets.el library and thus the Secret Service API when you specify a source matching "secrets:COLLECTION". For instance, you could use "secrets:session" to use the "session" collection, open only for the lifetime of Emacs. Or you could use "secrets:Login" to open the "Login" collection. As a special case, you can use the symbol default in auth-sources (not a string, but a symbol) to specify the "default" alias. Here is a contrived example that sets auth-sources to search three collections and then fall back to ~/.authinfo.gpg.

     (setq auth-sources '(default
                          "secrets:session"
                          "secrets:Login"
                          "~/.authinfo.gpg"))

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4 Help for developers

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

— Variable: auth-source-debug

Set this variable to 'trivia to see lots of output in *Messages*, or set it to a function that behaves like message to do your own logging.

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

— Function: auth-source-search &rest spec &key type max host user port secret require create delete &allow-other-keys

This function searches (or modifies) authentication backends according to spec. See the function's doc-string for details.

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

     (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)))

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 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, nnimap.el calls the :save-function like so:

     (when (functionp (nth 2 credentials))
        (funcall (nth 2 credentials)))

This will work whether the :save-function was provided or not. :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 :save-function will not run again (but it will log something if you have set auth-source-debug to '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 :create t is to call the :save-function if it's provided.

— Function: auth-source-delete &rest spec &key delete &allow-other-keys

This function deletes entries matching spec from the authentication backends. It returns the entries that were deleted. The backend may not actually delete the entries.

— Function: auth-source-forget spec

This function forgets any cached data that exactly matches spec. It returns t if it forget some data, and nil if no matching data was found.

— Function: auth-source-forget+ &rest spec &allow-other-keys

This function forgets any cached data matching spec. It returns the number of items forgotten.

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Appendix A GnuPG and EasyPG Assistant Configuration

If the auth-sources variable contains ~/.authinfo.gpg before ~/.authinfo, the auth-source library will try to read the GnuPG encrypted .gpg file first, before the unencrypted file.

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

     (require 'epa-file)
     (epa-file-enable)

If you want your GnuPG passwords to be cached, set up gpg-agent or EasyPG Assistant (see Caching Passphrases).

To quick start, here are some questions:

  1. Do you use GnuPG version 2 instead of GnuPG version 1?
  2. Do you use symmetric encryption rather than public key encryption?
  3. Do you want to use gpg-agent?

Here are configurations depending on your answers:

1 2 3 Configuration
Yes Yes Yes Set up gpg-agent.
Yes Yes No You can't, without gpg-agent.
Yes No Yes Set up gpg-agent.
Yes No No You can't, without gpg-agent.
No Yes Yes Set up elisp passphrase cache.
No Yes No Set up elisp passphrase cache.
No No Yes Set up gpg-agent.
No No No You can't, without gpg-agent.

To set up gpg-agent, follow the instruction in GnuPG manual (see Invoking GPG-AGENT).

To set up elisp passphrase cache, set epa-file-cache-passphrase-for-symmetric-encryption.

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Appendix B GNU Free Documentation License

Version 1.3, 3 November 2008
     Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     http://fsf.org/
     
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    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

  11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

  12. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       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, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

         with the Invariant Sections being list their titles, with
         the Front-Cover Texts being list, and with the Back-Cover Texts
         being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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