feat: add dokku-specific env vars

This change allows us to pass the ssh user and a proxy 'name' (mapping to the authenticating user) that will allow sshcommand to identify who is performing commands.

Author: josegonzalez

git-http-backend.go

@@ -119,13 +119,24 @@ func serviceRpc(hr HandlerReq) {
 	w.Header().Set("Content-Type", fmt.Sprintf("application/x-git-%s-result", rpc))
 	w.WriteHeader(http.StatusOK)
 
+	env := []string{
+		"SSH_USER=git-http-backend",
+	}
+
+	user, _, authok := r.BasicAuth()
+	if authok {
+		env = append(env, fmt.Sprintf("NAME=%s", user))
+		env = append(env, fmt.Sprintf("SSH_NAME=%s", user))
+	}
+
 	args := []string{rpc, "--stateless-rpc", dir}
 	cmd := exec.Command(config.GitBinPath, args...)
 	version := r.Header.Get("Git-Protocol")
 	if len(version) != 0 {
 		cmd.Env = append(os.Environ(), fmt.Sprintf("GIT_PROTOCOL=%s", version))
 	}
 	cmd.Dir = dir
+	cmd.Env = env
 	in, err := cmd.StdinPipe()
 	if err != nil {
 		log.Print(err)