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

static/directives/external-login-button.html

@@ -1,24 +1,14 @@
 <span class="external-login-button-element">
-  <span ng-if="provider == 'github'">
-    <a href="javascript:void(0)" ng-class="isLink ? '' : 'btn btn-primary btn-block'" quay-require="['GITHUB_LOGIN']" ng-click="startSignin('github')" style="margin-bottom: 10px" ng-disabled="signingIn">
-      <i class="fa fa-github fa-lg"></i>
-      <span ng-if="action != 'attach'">
-          Sign In with GitHub
-          <span ng-if="isEnterprise('github')">Enterprise</span>
-      </span>
-      <span ng-if="action == 'attach'">
-        Attach to GitHub
-        <span ng-if="isEnterprise('github')">Enterprise</span>
-        Account
-      </span>
-    </a>
-  </span>
-
-  <span ng-if="provider == 'google'">
-    <a href="javascript:void(0)" ng-class="isLink ? '' : 'btn btn-primary btn-block'" quay-require="['GOOGLE_LOGIN']"  ng-click="startSignin('google')" ng-disabled="signingIn">
-      <i class="fa fa-google fa-lg"></i>
-      <span ng-if="action != 'attach'">Sign In with Google</span>
-      <span ng-if="action == 'attach'">Attach to Google Account</span>
-    </a>
-  </span>
+  <a href="javascript:void(0)" ng-class="isLink ? '' : 'btn btn-primary btn-block'"
+     ng-if="providerInfo.enabled" ng-click="startSignin()" style="margin-bottom: 10px"
+     ng-disabled="signingIn">
+    <img ng-src="{{ providerInfo.icon().url }}" ng-if="providerInfo.icon().url">
+    <i class="fa" ng-class="providerInfo.icon().icon" ng-if="providerInfo.icon().icon"></i>
+    <span ng-if="action != 'attach'">
+        Sign In with {{ providerInfo.title() }}
+    </span>
+    <span ng-if="action == 'attach'">
+      Attach to {{ providerInfo.title() }}
+    </span>
+  </a>
 </span>