Using native validation if SSH-Agent is available.

[blaubaer]

Instead of using just checking if SSH_AUTH_SOCK we use sshagent.Available() which also checks in more platform dependent ways if an SSH-Agent is available and working. Especially on Windows this variable is usually not present but a Pageant or Windows OpenSSH-Agent might run already. Currently you can only work with them by setting some junk into this environment variable before running the service.

Scope of change

Sorry for the whole change of the file. It seems that in the repository there was initially the files stored with crlf (as reported by git ls-files --eol). I tried several ways to clean this up, but was not successful. Although the change itself is just focused on:

Old:

// authSSHAgent discovers environment for SSH_AUTH_SOCK and builds NewSSHAgentAuth
// If returned null - no agent was set up
func authSSHAgent(params *RequestMetadataParams) (*sshGit.PublicKeysCallback, error) {
	if _, ok := os.LookupEnv("SSH_AUTH_SOCK"); !ok {
		return nil, nil
	}

New:

import (
[..]
	sshagent "github.com/xanzy/ssh-agent"
[..]
)
[..]
// authSSHAgent discovers environment for SSH_AUTH_SOCK (or other platform dependent logic)
// and builds NewSSHAgentAuth.
//
// If returned null - no agent was set up
func authSSHAgent(params *RequestMetadataParams) (*sshGit.PublicKeysCallback, error) {
	if !sshagent.Available() {
		return nil, nil
	}

[dee-kryvenko]

Hey @blaubaer, thanks for the contribution! This looks great.

[dee-kryvenko]

Released in https://github.com/plumber-cd/terraform-backend-git/releases/tag/v0.0.17