pass-git-helper

A git credential helper implementation that allows using pass as the credential backend for your https-based git repositories. When git tries to interact with an https-based upstream and needs credentials, this helper will be called to look up the credentials from the user's password store. Instead of enforcing a specific layout of the password store, a configuration file with explicitly defining mappings between hosts and entries in the password store is used, giving full flexibility to the user on how to structure or reuse existing password databases for git authentication. pass-git-helper will use the mappings to find the correct entry in the user's password store based on the request URL and then provides git with the credentials from this entry.

Preconditions

It is recommended to configure GPG to use a graphical pinentry program. That way, you can also use this helper when git is invoked via GUI programs such as your IDE. For a configuration example, refer to the ArchWiki. In case you really want to use the terminal for pinentry (via pinentry-curses), be sure to appropriately configure the environment variable GPG_TTY, most likely by adding the following lines to your shell initialization:

GPG_TTY=$(tty)
export GPG_TTY

If you use this setup for remote work via SSH, also consider the alternative of GPG agent forwarding.

Installation

Official Packages

If possible, use an available package for your Linux distribution or operating system such as the ones linked below.

From Source

sudo pip install .

This might potentially install Python packages without the knowledge of your system's package manager. If all package preconditions are already met, you can also copy the script file to to your system to avoid this problem:

sudo cp passgithelper.py /usr/local/bin/pass-git-helper

Another option is to install the script in an isolated virtualenv:

virtualenv /your/env
/your/env/pip install .

Usage

Configure git to use pass-git-helper

To instruct git to use the helper, set the credential.helper configuration option of git to /full/path/to/pass-git-helper. In case you do not want to include a full path, a workaround using a shell fragment needs to be used, i.e. !pass-git-helper $@ must be the option value. The option can be set using the CLI with:

git config credential.helper '!pass-git-helper $@'

This will result in the following contents in ~/.gitconfig:

[credential]
    helper = !pass-git-helper $@

In case you share the ~/.gitconfig across multiple machines and pass-git-helper is not available on all of them, the following version does not bail out if pass git helper is missing:

[credential]
    helper = !type pass-git-helper >/dev/null && pass-git-helper $@

pass-git-helper can be combined with other helpers. For instance, the following configuration first tries the git built-in cache helper for in-memory password access before falling back to pass-git-helper if a cache miss occurs:

[credential]
    helper = cache
    helper = !type pass-git-helper >/dev/null && pass-git-helper$@

Define Mappings

Create the file ~/.config/pass-git-helper/git-pass-mapping.ini. This file uses ini syntax to specify the mapping of hosts to entries in the password store database. Section headers define patterns which are matched against the host part of a URL with a git repository. Matching supports wildcards (using the python fnmatch module). Each section needs to contain a target entry pointing to the entry in the password store with the password (and optionally username) to use.

Example:

[github.com*]
target=dev/github

[*.fooo-bar.*]
target=dev/fooo-bar

If you want to match entries not only based on the host, but also based on the path on a host, set credential.useHttpPath to true in your git config, e.g. via:

git config credential.useHttpPath true

Afterwards, entries can be matched against host.com/path/to/repo in the mapping. This means that in order to use a specific account for a certain Github project, you can then use the following mapping pattern:

[github.com/username/project*]
target=dev/github

Please note that when including the path in the mapping, the mapping expressions need to match against the whole path. As a consequence, in case you want to use the same account for all Github projects, you need to make sure that a wildcard covers the path of the URL, as shown here:

[github.com*]
target=dev/github

The host can be used as a variable to address a pass entry. This is especially helpful for wildcard matches:

[*]
target=git-logins/${host}

The above configuration directive will lead to any host that did not match any previous section in the ini file to being looked up under the git-logins directory in your password store.

DEFAULT Section

Defaults suitable for all entries of the mapping file can be specified in a special section of the configuration file named [DEFAULT]. Everything configure in this section will automatically be available for all further entries in the file, but can be overridden there, too.

Using Different Mappings Depending on the Working Directory

Using the includeIf directive available in git >= 2.13, it is possible to perform matching based on the current working directory by invoking pass-git-helper with a conditional MAPPING-FILE. To achieve this, edit your .gitconfig, e.g. like this:

[includeIf "gitdir:~/src/user1/"]
    path=~/.config/git/gitconfig_user1
[includeIf "gitdir:~/src/user2/"]
    path=~/.config/git/gitconfig_user2

With the following contents of gitconfig_user1 (and gitconfig_user2 respectively), mapping_user1.ini, which could contain a target entry to e.g. github.com/user1 would always be invoked in ~/src/user1:

[user]
    name = user1
[credential]
    helper=/full/path/to/pass-git-helper -m /full/path/to/mapping_user1.ini

See also the official documentation for .gitconfig.

Switching Password Stores per Mapping

To select a different password store for certain entries, the password_store_dir configuration key can be set. If set, pass is directed to a different data directory by defining the PASSWORD_STORE_DIR environment variable when calling pass.

The following config demonstrates this practices

[github.com/mycompany]
password_store_dir=/home/me/.work-passwords

Password Store Layout and Data Extraction

Password

As usual with pass, this helper assumes that the password is contained in the first line of the password store entry. Though uncommon, it is possible to strip a prefix from the data of the first line (such as password: by specifying an amount of characters to leave out in the skip_password field for an entry or also in the [DEFAULT] section to apply for all entries:

[DEFAULT]
# length of "password: "
skip_password=10

[somedomain]
# for some reasons, this entry doesn't have a password prefix
skip_password=0
target=special/noprefix

Username

pass-git-helper can also provide the username necessary for authenticating at a server. In contrast to the password, no clear convention exists how username information is stored in password entries. Therefore, multiple strategies to extract the username are implemented and can be selected globally for the whole password store in the [DEFAULT] section, or individually for certain entries using the username_extractor key:

[DEFAULT]
username_extractor=regex_search
regex_username=^user: (.*)$

[differingdomain.com]
# use a fixed line here instead of a regex search
username_extractor=specific_line
line_username=1

The following strategies can be configured:

Strategy "specific_line" (default)

Extracts the data from a line indexed by its line number. Optionally a fixed-length prefix can be stripped before returning the line contents.

Configuration:

• line_username: Line number containing the username, 0-based. Default: 1 (second line)
• skip_username: Number of characters to skip at the beginning of the line, for instance to skip a user: prefix. Similar to skip_password. Default: 0.

Strategy "regex_search"

Searches for the first line that matches a provided regular expressions and returns the contents of that line that are captured in a regular expression capture group.

Configuration:

• regex_username: The regular expression to apply. Has to contain a single capture group for indicating the data to extract. Default: ^username: +(.*)$.

Strategy "entry_name"

Returns the last path fragment of the password store entry as the username. For instance, if a regular pass call would be pass show dev/github.com/languitar, the returned username would be languitar.

No configuration options.

File Encoding

By default, password store entries are assumed to use UTF-8 encoding. If all or some of your entries use a different encoding, use the encoding key (for instance, in the DEFAULT section) to specify the used encoding.

Command Line Options

-l can be given as an option to the script to produce logging output on stderr. This might be useful to understand how the mapping is applied.

-m MAPPING_FILE can be specified to use an alternative mapping file location.

Skipping Processing

In some automated contexts it might be necessary to prevent GPG from asking for the passphrase (via the agent). To achieve this, you can disable the complete processing of this helper by defining the environment variable PASS_GIT_HELPER_SKIP with any content (or no content at all). pass-git-helper will return immediately in this case, indicating to git that no suitable credentials could be found.

License

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or any later version. This work is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.