diff --git a/app/controllers/omniauth_callbacks_controller.rb b/app/controllers/omniauth_callbacks_controller.rb
index 689d2e3db22..d631d09f1b8 100644
--- a/app/controllers/omniauth_callbacks_controller.rb
+++ b/app/controllers/omniauth_callbacks_controller.rb
@@ -112,6 +112,8 @@ class OmniauthCallbacksController < Devise::OmniauthCallbacksController
 
       continue_login_process
     end
+  rescue Gitlab::OAuth::SigninDisabledForProviderError
+    handle_disabled_provider
   rescue Gitlab::OAuth::SignupDisabledError
     handle_signup_error
   end
@@ -168,6 +170,13 @@ class OmniauthCallbacksController < Devise::OmniauthCallbacksController
     redirect_to new_user_session_path
   end
 
+  def handle_disabled_provider
+    label = Gitlab::OAuth::Provider.label_for(oauth['provider'])
+    flash[:alert] = "Signing in using #{label} has been disabled"
+
+    redirect_to new_user_session_path
+  end
+
   def log_audit_event(user, options = {})
     AuditEventService.new(user, user, options)
       .for_authentication.security_event
diff --git a/changelogs/unreleased/jej-fix-disabled-oauth-access.yml b/changelogs/unreleased/jej-fix-disabled-oauth-access.yml
new file mode 100644
index 00000000000..3a92c432dc6
--- /dev/null
+++ b/changelogs/unreleased/jej-fix-disabled-oauth-access.yml
@@ -0,0 +1,5 @@
+---
+title: Prevent OAuth login POST requests when a provider has been disabled
+merge_request:
+author:
+type: security
diff --git a/lib/gitlab/o_auth.rb b/lib/gitlab/o_auth.rb
new file mode 100644
index 00000000000..5ad8d83bd6e
--- /dev/null
+++ b/lib/gitlab/o_auth.rb
@@ -0,0 +1,6 @@
+module Gitlab
+  module OAuth
+    SignupDisabledError = Class.new(StandardError)
+    SigninDisabledForProviderError = Class.new(StandardError)
+  end
+end
diff --git a/lib/gitlab/o_auth/user.rb b/lib/gitlab/o_auth/user.rb
index d33f33d192f..fff9360ea27 100644
--- a/lib/gitlab/o_auth/user.rb
+++ b/lib/gitlab/o_auth/user.rb
@@ -5,8 +5,6 @@
 #
 module Gitlab
   module OAuth
-    SignupDisabledError = Class.new(StandardError)
-
     class User
       attr_accessor :auth_hash, :gl_user
 
@@ -29,7 +27,8 @@ module Gitlab
       end
 
       def save(provider = 'OAuth')
-        unauthorized_to_create unless gl_user
+        raise SigninDisabledForProviderError if oauth_provider_disabled?
+        raise SignupDisabledError unless gl_user
 
         block_after_save = needs_blocking?
 
@@ -226,8 +225,10 @@ module Gitlab
         Gitlab::AppLogger
       end
 
-      def unauthorized_to_create
-        raise SignupDisabledError
+      def oauth_provider_disabled?
+        Gitlab::CurrentSettings.current_application_settings
+                               .disabled_oauth_sign_in_sources
+                               .include?(auth_hash.provider)
       end
     end
   end
diff --git a/spec/controllers/omniauth_callbacks_controller_spec.rb b/spec/controllers/omniauth_callbacks_controller_spec.rb
new file mode 100644
index 00000000000..c639ad32ec6
--- /dev/null
+++ b/spec/controllers/omniauth_callbacks_controller_spec.rb
@@ -0,0 +1,75 @@
+require 'spec_helper'
+
+describe OmniauthCallbacksController do
+  include LoginHelpers
+
+  let(:user) { create(:omniauth_user, extern_uid: 'my-uid', provider: provider) }
+  let(:provider) { :github }
+
+  before do
+    mock_auth_hash(provider.to_s, 'my-uid', user.email)
+    stub_omniauth_provider(provider, context: request)
+  end
+
+  it 'allows sign in' do
+    post provider
+
+    expect(request.env['warden']).to be_authenticated
+  end
+
+  shared_context 'sign_up' do
+    let(:user) { double(email: 'new@example.com') }
+
+    before do
+      stub_omniauth_setting(block_auto_created_users: false)
+    end
+  end
+
+  context 'sign up' do
+    include_context 'sign_up'
+
+    it 'is allowed' do
+      post provider
+
+      expect(request.env['warden']).to be_authenticated
+    end
+  end
+
+  context 'when OAuth is disabled' do
+    before do
+      stub_env('IN_MEMORY_APPLICATION_SETTINGS', 'false')
+      settings = Gitlab::CurrentSettings.current_application_settings
+      settings.update(disabled_oauth_sign_in_sources: [provider.to_s])
+    end
+
+    it 'prevents login via POST' do
+      post provider
+
+      expect(request.env['warden']).not_to be_authenticated
+    end
+
+    it 'shows warning when attempting login' do
+      post provider
+
+      expect(response).to redirect_to new_user_session_path
+      expect(flash[:alert]).to eq('Signing in using GitHub has been disabled')
+    end
+
+    it 'allows linking the disabled provider' do
+      user.identities.destroy_all
+      sign_in(user)
+
+      expect { post provider }.to change { user.reload.identities.count }.by(1)
+    end
+
+    context 'sign up' do
+      include_context 'sign_up'
+
+      it 'is prevented' do
+        post provider
+
+        expect(request.env['warden']).not_to be_authenticated
+      end
+    end
+  end
+end
diff --git a/spec/features/oauth_login_spec.rb b/spec/features/oauth_login_spec.rb
index 49d8e52f861..a5e325ee2e3 100644
--- a/spec/features/oauth_login_spec.rb
+++ b/spec/features/oauth_login_spec.rb
@@ -10,8 +10,7 @@ feature 'OAuth Login', :js, :allow_forgery_protection do
 
   def stub_omniauth_config(provider)
     OmniAuth.config.add_mock(provider, OmniAuth::AuthHash.new(provider: provider.to_s, uid: "12345"))
-    set_devise_mapping(context: Rails.application)
-    Rails.application.env_config['omniauth.auth'] = OmniAuth.config.mock_auth[provider]
+    stub_omniauth_provider(provider)
   end
 
   providers = [:github, :twitter, :bitbucket, :gitlab, :google_oauth2,
diff --git a/spec/support/devise_helpers.rb b/spec/support/devise_helpers.rb
index 890a2d9d287..66874e10f38 100644
--- a/spec/support/devise_helpers.rb
+++ b/spec/support/devise_helpers.rb
@@ -2,13 +2,16 @@ module DeviseHelpers
   # explicitly tells Devise which mapping to use
   # this is needed when we are testing a Devise controller bypassing the router
   def set_devise_mapping(context:)
-    env =
-      if context.respond_to?(:env_config)
-        context.env_config
-      elsif context.respond_to?(:env)
-        context.env
-      end
+    env = env_from_context(context)
 
     env['devise.mapping'] = Devise.mappings[:user] if env
   end
+
+  def env_from_context(context)
+    if context.respond_to?(:env_config)
+      context.env_config
+    elsif context.respond_to?(:env)
+      context.env
+    end
+  end
 end
diff --git a/spec/support/login_helpers.rb b/spec/support/login_helpers.rb
index 50702a0ac88..b52b6a28c54 100644
--- a/spec/support/login_helpers.rb
+++ b/spec/support/login_helpers.rb
@@ -125,6 +125,13 @@ module LoginHelpers
     })
   end
 
+  def stub_omniauth_provider(provider, context: Rails.application)
+    env = env_from_context(context)
+
+    set_devise_mapping(context: context)
+    env['omniauth.auth'] = OmniAuth.config.mock_auth[provider]
+  end
+
   def stub_omniauth_saml_config(messages)
     set_devise_mapping(context: Rails.application)
     Rails.application.routes.disable_clear_and_finalize = true