document how to inject git credentials in common CI systems

This patch documents how to easily inject git credentials
in the Github Actions CI, as well as in Gitlab CI.

Signed-off-by: Felix Moessbauer <[email protected]>
Signed-off-by: Jan Kiszka <[email protected]>

docs/userguide/credentials.rst

@@ -30,11 +30,33 @@ Git Configuration
 A ``.gitconfig`` file can be used to provide credentials as well as
 url rewrites of git repositories (``insteadof``). To support the patching
 of git repositories, kas injects a ``[user]`` section, possibly overwriting
-an existing one. When running in the Github CI, the ``.gitconfig`` file is
-automatically injected. In addition, credential helpers can be used by
+an existing one. In addition, credential helpers can be used by
 setting the corresponding environment variables. These are added to the
 ``.gitconfig`` file as well.
 
+Github Actions
+~~~~~~~~~~~~~~
+
+When running in a Github Action, the ``.gitconfig`` file is automatically
+injected. In combination with the
+`webfactory/ssh-agent <https://github.com/webfactory/ssh-agent>`_ action,
+this automatically makes the required credentials available to kas and
+bitbake.
+
+Gitlab CI
+~~~~~~~~~
+
+When running in the Gitlab CI, the ``CI_JOB_TOKEN`` can be used to access
+git repositories via https. kas automatically adds this token to the
+``.netrc`` file, where it is picked up by git. To be able to clone via ssh
+locally, but via https in the CI, a rewrite rule needs to be added to the
+``KAS_PREMIRRORS`` CI environment variable. Example:
+
+.. code-block:: yaml
+
+  variables:
+    KAS_PREMIRRORS: "git@${CI_SERVER_HOST}: https://${CI_SERVER_HOST}/"
+
 Netrc File
 ----------