SCP Workflow on Windows

[dokempf]

Thanks for providing this action, I am a very happy user!

I have recently stumbled across an issue on Windows with one of my use cases: I am using the action to set up a private key, which I then use to copy large, non-public files with scp from a VM hosted at my institution to the GitHub runner. The workflow works fine on Linux. On Windows, the action itself is successful, but the scp operation in a subsequent step fails with Permission denied (publickey)..

After reading carefully through #63 I was able to actually fix the problem by replacing my plain usage of scp on Windows with c://progra~1//git//usr//bin//scp.exe. I am happy to have found this fix, but I really do not like it. I would prefer it if this action could modify the environment such that the correct versions of SSH-related executables are picked up. I can imagine this in both an implicit way (like modifying path variables) or an explicit way (like export e.g. an SCP_BIN environment variable for the user to use).

Feel free to ignore and close this if you consider it out of scope of the action.

[mpdude]

I was trying to focus the action on setting up the SSH Agent, so I am a bit reluctant to do more than strictly necessary. After all, all that needs to be maintained and fixed for various platforms in the long run.

I would, however, very much welcome a PR that adds a short problem explanation and possible workaround to the https://github.com/webfactory/ssh-agent#additional-information-for-particular-tools-or-platforms section of the README.

Would you want to do that?