Pass username to OAuth2 login flow

Closes MBL-5463

Test Plan:
GET login/oauth2/auth using the appropriate params for your canvas
install + the new param of `unique_id={username}`
Ensure that the username provided as a param is automatically populated
into the username field of login form.

Change-Id: I2d226953186cff2fecc5a19cbadd8627013481e8
Reviewed-on: https://gerrit.instructure.com/74208
QA-Review: Ben Kirato <benk@instructure.com>
Reviewed-by: Cameron Sutter <csutter@instructure.com>
Tested-by: Jenkins
Product-Review: Peyton Craighill <pcraighill@instructure.com>

app/controllers/login_controller.rb

@@ -78,7 +78,9 @@ class LoginController < ApplicationController
     end
 
     unless flash[:delegated_message]
-      return redirect_to url_for({ controller: "login/#{auth_type}", action: :new }.merge(params.slice(:id)))
+      return redirect_to url_for({ controller: "login/#{auth_type}", action: :new }
+                                     .merge(params.slice(:id))
+                                     .merge(params.slice(:pseudonym_session)))
     end
 
     # we had an error from an SSO - we need to show it

app/controllers/oauth2_provider_controller.rb

@@ -45,7 +45,9 @@ class Oauth2ProviderController < ApplicationController
     if @current_pseudonym && !params[:force_login]
       redirect_to Canvas::Oauth::Provider.confirmation_redirect(self, provider, @current_user)
     else
-      redirect_to login_url(params.slice(:canvas_login, :pseudonym_session, :force_login, :authentication_provider))
+      params["pseudonym_session"] = {"unique_id" => params[:unique_id]} if params.key?(:unique_id)
+      redirect_to login_url(params.slice(:canvas_login, :pseudonym_session, :force_login,
+                                         :authentication_provider, :pseudonym_session))
     end
   end
 

doc/api/oauth_endpoints.md

@@ -77,6 +77,11 @@ wrong person in, as <a href="http://homakov.blogspot.com/2012/07/saferweb-most-c
       if a user already has an active Canvas web session, they will not be
       asked to re-enter their credentials.</td>
     </tr>
+    <tr>
+      <td class="mono">unique_id<span class="label optional"></span></td>
+      <td>Set to the user's username to be populated in the login form in the event
+      that the user must authenticate.</td>
+    </tr>
   </tbody>
 </table>
 

spec/controllers/login_controller_spec.rb

@@ -107,6 +107,12 @@ describe LoginController do
       get 'new', authentication_provider: ap2.id
       expect(response).to redirect_to(controller.url_for(controller: 'login/cas', action: :new, id: ap2.id))
     end
+
+    it "should pass pseudonym_session[unique_id] to redirect to populate username textbox" do
+      get 'new', "pseudonym_session" => {"unique_id"=>"test"}
+      expect(response).to redirect_to(
+        controller.url_for(controller: 'login/canvas', action: :new)+'?pseudonym_session%5Bunique_id%5D=test')
+    end
   end
 
   describe "#logout" do

spec/controllers/oauth2_provider_controller_spec.rb

@@ -44,6 +44,12 @@ describe Oauth2ProviderController do
       expect(response).to redirect_to(login_url(:canvas_login => 1))
     end
 
+    it 'should pass pseudonym_session[unique_id] to login to populate username textbox' do
+      get :auth, :client_id => key.id, :redirect_uri => Canvas::Oauth::Provider::OAUTH2_OOB_URI,
+          "unique_id"=>"test", :force_login => true
+      expect(response).to redirect_to(login_url+'?force_login=true&pseudonym_session%5Bunique_id%5D=test')
+    end
+
     context 'with a user logged in' do
       before :once do
         user_with_pseudonym(:active_all => 1, :password => 'qwerty')
@@ -93,6 +99,7 @@ describe Oauth2ProviderController do
         expect(response).to be_redirect
         expect(response.location).to match(/https:\/\/example.com/)
       end
+
     end
   end