Add custom docker registry authentication (#665)

* Add custom docker registry authentication

Uses DOCKER_USERNAME and DOCKER_PASSWORD as secrets provided into
the act cli.

Closes #527

Co-authored-by: Björn Brauer <zaubernerd@zaubernerd.de>

* Add test to check if pull authentication is filled in

* Update debug message to be more descriptive

Co-authored-by: Ryan (hackercat) <me@hackerc.at>

Co-authored-by: Björn Brauer <zaubernerd@zaubernerd.de>
Co-authored-by: Ryan (hackercat) <me@hackerc.at>

pkg/runner/run_context.go

@@ -118,6 +118,8 @@ func (rc *RunContext) startJobContainer() common.Executor {
 			Entrypoint:  []string{"/usr/bin/tail", "-f", "/dev/null"},
 			WorkingDir:  rc.Config.ContainerWorkdir(),
 			Image:       image,
+			Username:    rc.Config.Secrets["DOCKER_USERNAME"],
+			Password:    rc.Config.Secrets["DOCKER_PASSWORD"],
 			Name:        name,
 			Env:         envList,
 			Mounts:      mounts,

pkg/runner/step_context.go

@@ -247,6 +247,8 @@ func (sc *StepContext) newStepContainer(ctx context.Context, image string, cmd [
 		Entrypoint:  entrypoint,
 		WorkingDir:  rc.Config.ContainerWorkdir(),
 		Image:       image,
+		Username:    rc.Config.Secrets["DOCKER_USERNAME"],
+		Password:    rc.Config.Secrets["DOCKER_PASSWORD"],
 		Name:        createContainerName(rc.jobContainerName(), step.ID),
 		Env:         envList,
 		Mounts:      mounts,