Adds handling of 401 for POST /v2/token without authentication

This fix adds support for image registries that expect authentication for POST /v2/token such as used by the GET. E.g., JFrog Artifactory y has been observed to respond with a 401 (Unauthorized) in that case. Adding 401 in addition to the current handling of 405 and 404 in the resolver solves the authentication problem. Finally, this enables image pulls also for Artifactory.

Signed-off-by: Ruediger Maass <ruediger.maass@de.ibm.com>

remotes/docker/resolver.go

@@ -498,7 +498,8 @@ func (r *dockerBase) fetchTokenWithOAuth(ctx context.Context, to tokenOptions) (
 
 	// Registries without support for POST may return 404 for POST /v2/token.
 	// As of September 2017, GCR is known to return 404.
-	if (resp.StatusCode == 405 && r.username != "") || resp.StatusCode == 404 {
+	// As of February 2018, JFrog Artifactory is known to return 401.
+	if (resp.StatusCode == 405 && r.username != "") || resp.StatusCode == 404 || resp.StatusCode == 401 {
 		return r.getToken(ctx, to)
 	} else if resp.StatusCode < 200 || resp.StatusCode >= 400 {
 		b, _ := ioutil.ReadAll(io.LimitReader(resp.Body, 64000)) // 64KB