Provide option to only configure auth

[btashton]

I'm facing an issue where I have a git repo passed via an artifact or cache from another job in the workflow. I need to be able to run git command on this including pulling tags, but the auth does not seem to travel with it (even with persist enabled [worked at one point but not now]). I do not want to go through the process of checking out the repo and especially want to keep the ref as it is.

Right now I have to do something like this:

      - name: Export  Repo SHA
        run:  echo "::set-env name=rep_sha::`git -C sources/myrepo rev-parse HEAD`"
      - name: Refresh Git Credentials
        uses: actions/checkout@v2
        with:
          repository: org/repo
          ref: ${{ env.repo_sha }}
          path: sources/myrep
          fetch-depth: 1
      - name: Get Tags for Repo
        run: git -C sources/myrepo fetch --tags

Doing this still causes it to reach out via the checkout action and it requires me to fetch the rev in the previous step.

[ericsciple]

It should be pretty cheap to fetch, since all of the git objects already exist?

[btashton]

@ericsciple unfortunately there is a lot more that goes on including things like Removing previously created refs, to avoid conflicts This whole flow adds 10's of seconds for no reason.

[btashton]

@ericsciple in our larger repo this is getting annoying because all the refs are getting "cleaned" and have to be pulled again.
This flow is now up to 90sec for something I would expect to be nearly free.

Run actions/checkout@v2
Syncing repository: apache/incubator-nuttx
Getting Git version info
/usr/local/bin/git config --local --get remote.origin.url
https://github.com/apache/incubator-nuttx
Removing previously created refs, to avoid conflicts
Cleaning the repository
Disabling automatic garbage collection
Setting up auth
Fetching the repository
Determining the checkout info
Checking out the ref
/usr/local/bin/git log -1