This bundle provides optional support for communicating with an SSH agent for SSH or SFTP authentication. It is an OSGi fragment for bundle org.eclipse.jgit.ssh.apache, and it provides transports for local communication with SSH agents.
On Linux, OS X, and BSD, the only transport mechanism supported is the usual communication via a Unix domain socket. This is the only protocol the OpenSSH SSH agent supports. A Unix domain socket appears as a special file in the file system; this file name is typically available in the environment variable SSH_AUTH_SOCK.
The SSH config IdentityAgent can be set to this socket filename to specify exactly which Unix domain socket to use, or it can be set to SSH_AUTH_SOCK to use the value from that environment variable. If IdentityAgent is not set at all, JGit uses SSH_AUTH_SOCK by default. If the variable is not set, no SSH agent will be used. IdentityAgent can also be set to none to not use any SSH agent.
On Windows, two different transports are supported:
Possible settings of IdentityAgent to select a particular transport are
//./pipe/openssh-ssh-agent: the Windows named pipe of Win32-OpenSSH.//./pageant: the shared-memory mechanism of Pageant.none: do not use any SSH agent.//./pipe/<any_valid_pipe_name>: use a specific Windows named pipe.The default transport on Windows if IdentityAgent is not set at all is the Pageant shared-memory transport. Environment variable SSH_AUTH_SOCK needs not be set for Pageant, and must not be set for Win32-OpenSSH.
It is also possible to use a named pipe as transport for Pageant (as of version 0.75). Unfortunately, Pageant unnecessarily cryptographically obfuscates the pipe name, so it is not possible for JGit to determine it automatically. The pipe name is pageant.<user name>.<sha256>, for instance pageant.myself.c5687736ba755a70b000955cb191698aed7db221c2b0710199eb1f5298922ab5. A user can look up the name by starting Pageant and then running the command dir \\.\pipe\\ in a command shell. Once the name is known, setting IdentityAgent to the pipe name as //./pipe/pageant.myself.c5687736ba755a70b000955cb191698aed7db221c2b0710199eb1f5298922ab5 makes JGit use this Windows named pipe for communication with Pageant.
(You can use forward slashes in the ~/.ssh/config file. SSH config file parsing has its own rules about backslashes in config files; which are treated as escape characters in some contexts. With backslashes one would have to write, e.g., \\\\.\pipe\openssh-ssh-agent.)
With these two transport mechanisms, Pageant and Win32-OpenSSH are supported. As for GPG: the gpg-agent can be configured to emulate ssh-agent (presumably via a WinSockets2 “Unix domain socket” on Windows) or to emulate Pageant (using the shared memory mechanism). Running gpg-agent with the enable-ssh-support option is reported not to work on Windows, though. But the PuTTY emulation in gpg-agent (option enable-putty-support) should work, so it should be possible to use gpg-agent instead of Pageant.
Neither Pageant (as of version 0.76) nor Win32-OpenSSH (as of version 8.6) support the confirm or lifetime constraints for AddKeysToAgent. gpg-agent apparently does, even when communicating over the Pageant shared memory mechanism.
The ssh-agent from git bash on Windows is currently not supported. It would need a connector handling Cygwin socket files and the Cygwin handshake over a TCP stream socket bound to the loopback interface. The Cygwin socket file is exposed in the Windows file system at %TEMP%\ssh-XXXXXXXXXX\agent.<number>, but it does not have a fixed name (the X's and the number are variable and change each time ssh-agent is started).
The implementation of all transports uses JNA.