Can't access to Gitlab Docker Registry using an Oauth access token (with read_registry scope enabled)

Summary

I have a situation where users have explicity authorized my application to read the Gitlab Docker Registry, but I can't login to the registry without asking for additional credentials (user's password or personal access tokens).

Steps to reproduce

1. Authorize an oauth application to access to read Gitlab Docker Registry (read_registry scope)
2. Exchange the code for an oauth access token with read_registry enabled
3. Use the Oauth access token to try to login to the Gitlab Docker Registry (registry.gitlab.com)

What is the current bug behavior?

1. The user explicitly authorize my application to read the Gitlab Docker Registry
2. I exchanged the code for an OAuth access token:

API endpoint: https://gitlab.com/oauth/token Response: '{"access_token":"","token_type":"bearer","refresh_token":"","scope":"api read_user read_registry","created_at":1509442401}'

   As you can see the response confirms that I have access to the read_registry scope.

1. There is no way I can use the access token to login to the docker registry.

Tried:

* docker login -u *username* -p *user_password* registry.gitlab.com
  
It works

* docker login -u *email* -p *user_password* registry.gitlab.com
  
It works

* docker login -u gitlab-ci-token -p *personal_access_token* registry.gitlab.com
  
It works

* docker login -u gitlab-ci-token -p *oauth_access_token* registry.gitlab.com
  
It doesn't work :(

### What is the expected *correct* behavior?

If the user has authorized my application to read the Gitlab Docker Registry, there is no need to ask for additional permissions (user password or a personal access token) to access the Registry.

### Relevant logs and/or screenshots

![Selección_425](/uploads/f919e59b85a01e744489b817c9548ff1/Selección_425.png)

### Output of checks

This bug happens on GitLab.com

### Possible fixes

If the oauth access token has access to the read_registry scope, the docker container registry should accept this token for authentication.