Make new `allow_single_sign_on` feature backwards compatible

lib/gitlab/o_auth/user.rb

@@ -106,7 +106,11 @@ module Gitlab
 
       def signup_enabled?
         providers = Gitlab.config.omniauth.allow_single_sign_on
+        if providers.is_a?(Array)
           providers.include?(auth_hash.provider)
+        else
+          providers
+        end
       end
 
       def block_after_signup?

spec/lib/gitlab/o_auth/user_spec.rb

@@ -41,7 +41,7 @@ describe Gitlab::OAuth::User, lib: true do
 
     describe 'signup' do
       shared_examples "to verify compliance with allow_single_sign_on" do
-        context "with allow_single_sign_on enabled" do
+        context "with new allow_single_sign_on enabled syntax" do
           before { stub_omniauth_config(allow_single_sign_on: ['twitter']) }
 
           it "creates a user from Omniauth" do
@@ -54,12 +54,32 @@ describe Gitlab::OAuth::User, lib: true do
           end
         end
 
-        context "with allow_single_sign_on disabled (Default)" do
+        context "with old allow_single_sign_on enabled syntax" do
+          before { stub_omniauth_config(allow_single_sign_on: true) }
+
+          it "creates a user from Omniauth" do
+            oauth_user.save
+
+            expect(gl_user).to be_valid
+            identity = gl_user.identities.first
+            expect(identity.extern_uid).to eql uid
+            expect(identity.provider).to eql 'twitter'
+          end
+        end
+
+        context "with new allow_single_sign_on disabled syntax" do
           before { stub_omniauth_config(allow_single_sign_on: []) }
           it "throws an error" do
             expect{ oauth_user.save }.to raise_error StandardError
           end
         end
+
+        context "with old allow_single_sign_on disabled (Default)" do
+          before { stub_omniauth_config(allow_single_sign_on: false) }
+          it "throws an error" do
+            expect{ oauth_user.save }.to raise_error StandardError
+          end
+        end
       end
 
       context "with auto_link_ldap_user disabled (default)" do

spec/lib/gitlab/saml/user_spec.rb

@@ -61,7 +61,7 @@ describe Gitlab::Saml::User, lib: true do
         end
 
         context 'with allow_single_sign_on disabled' do
-          before { stub_omniauth_config(allow_single_sign_on: []) }
+          before { stub_omniauth_config(allow_single_sign_on: false) }
           it 'should throw an error' do
             expect{ saml_user.save }.to raise_error StandardError
           end