Add support for Dex to Quay

Fixes #306

- Adds support for Dex as an OAuth external login provider
- Adds support for OIDC in general
- Extract out external logins on the JS side into a service
- Add a feature flag for disabling direct login
- Add support for directing to the single external login service
- Does *not* yet support the config in the superuser tool

data/migrations/versions/3a3bb77e17d5_add_support_for_dex_login.py

@@ -0,0 +1,26 @@
+"""Add support for Dex login
+
+Revision ID: 3a3bb77e17d5
+Revises: 9512773a4a2
+Create Date: 2015-09-04 15:57:38.007822
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '3a3bb77e17d5'
+down_revision = '9512773a4a2'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade(tables):
+  op.bulk_insert(tables.loginservice, [{'id': 7, 'name': 'dex'}])
+
+
+def downgrade(tables):
+  op.execute(
+    tables.loginservice.delete()
+    .where(tables.loginservice.c.name == op.inline_literal('dex'))
+  )
+