diff --git a/README.md b/README.md
index 31a4751..5516522 100644
--- a/README.md
+++ b/README.md
@@ -258,10 +258,10 @@ Issue Trackers
 * Project id is the identifier of your project, i.e. **awesomeapp** for project at https://mingle.example.com/projects/awesomeapp
 * Card properties are comma separated key value pairs. You must specify a 'card_type', but anything else is optional. i.e. card_type = Defect, status = Open, priority = Essential
 
-**Github Issues Integration**
+**GitHub Issues Integration**
 
 * For 'Account/Repository', the account will either be a username or organization. i.e. **errbit/errbit**
-* You will also need to provide your username and password for your Github account.
+* You will also need to provide your username and password for your GitHub account.
   * (We'd really appreciate it if you wanted to help us implement OAuth instead!)
 
 
@@ -271,23 +271,23 @@ What if Errbit has an error?
 Errbit will log it's own errors to an internal app named **Self.Errbit**.
 The **Self.Errbit** app will be automatically created whenever the first error happens.
 
-If your Errbit instance has logged an error, we would appreciate a bug report on Github Issues.
+If your Errbit instance has logged an error, we would appreciate a bug report on GitHub Issues.
 You can post this manually at [https://github.com/errbit/errbit/issues](https://github.com/errbit/errbit/issues),
-or you can set up the Github Issues tracker for your **Self.Errbit** app:
+or you can set up the GitHub Issues tracker for your **Self.Errbit** app:
 
   1. Go to the **Self.Errbit** app's edit page. If that app does not exist yet, go to the apps page and click **Add a new App** to create it. (You can also create it by running `rake airbrake:test`.)
 
-  2. In the **Issue Tracker** section, click **Github Issues**.
+  2. In the **Issue Tracker** section, click **GitHub Issues**.
 
   3. Fill in the **Account/Repository** field with **errbit/errbit**.
 
   4. Fill in the **Username** field with your github username.
 
-  5. If you are logged in on [Github](https://github.com), you can find your **API Token** on this page: [https://github.com/account/admin](https://github.com/account/admin).
+  5. If you are logged in on [GitHub](https://github.com), you can find your **API Token** on this page: [https://github.com/account/admin](https://github.com/account/admin).
 
   6. Save the settings by clicking **Update App** (or **Add App**)
 
-  7. You can now easily post bug reports to Github Issues by clicking the **Create Issue** button on a **Self.Errbit** error.
+  7. You can now easily post bug reports to GitHub Issues by clicking the **Create Issue** button on a **Self.Errbit** error.
 
 
 TODO
diff --git a/app/controllers/users/omniauth_callbacks_controller.rb b/app/controllers/users/omniauth_callbacks_controller.rb
index f41fdd3..7b629e8 100644
--- a/app/controllers/users/omniauth_callbacks_controller.rb
+++ b/app/controllers/users/omniauth_callbacks_controller.rb
@@ -1,32 +1,32 @@
 class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
   def github
-    github_login = request.env["omniauth.auth"].extra.raw_info.login
-    github_token = request.env["omniauth.auth"].credentials.token
+    github_login = env["omniauth.auth"].extra.raw_info.login
+    github_token = env["omniauth.auth"].credentials.token
     github_user  = User.where(:github_login => github_login).first
 
     # If user is already signed in, link github details to their account
     if current_user
       # ... unless a user is already registered with same github login
       if github_user && github_user != current_user
-        flash[:error] = "User already registered with Github login '#{github_login}'"
-        redirect_to user_path(current_user)
+        flash[:error] = "User already registered with GitHub login '#{github_login}'"
       else
         # Add github details to current user
         current_user.update_attributes(
           :github_login       => github_login,
           :github_oauth_token => github_token
         )
-        flash[:success] = "Successfully linked Github account!"
-        redirect_to user_path(current_user)
+        flash[:success] = "Successfully linked GitHub account!"
       end
-
+      # User must have clicked 'link account' from their user page, so redirect there.
+      redirect_to user_path(current_user)
     elsif github_user
       # Store OAuth token
-      @user.update_attribute :github_oauth_token, request.env["omniauth.auth"].credentials.token
+      github_user.update_attribute :github_oauth_token, github_token
 
-      flash[:success] = I18n.t "devise.omniauth_callbacks.success", :kind => "Github"
-      sign_in_and_redirect @user, :event => :authentication
+      flash[:success] = I18n.t "devise.omniauth_callbacks.success", :kind => "GitHub"
+      sign_in_and_redirect github_user, :event => :authentication
     else
+      flash[:error] = "There are no authorized users with GitHub login '#{github_login}'. Please ask an administrator to register your user account."
       redirect_to new_user_session_path
     end
   end
diff --git a/app/models/issue_trackers/github_issues_tracker.rb b/app/models/issue_trackers/github_issues_tracker.rb
index b54d70f..24d02a1 100644
--- a/app/models/issue_trackers/github_issues_tracker.rb
+++ b/app/models/issue_trackers/github_issues_tracker.rb
@@ -6,7 +6,7 @@ class IssueTrackers::GithubIssuesTracker < IssueTracker
       :placeholder => "errbit/errbit from https://github.com/errbit/errbit"
     }],
     [:username, {
-      :placeholder => "Your username on Github"
+      :placeholder => "Your username on GitHub"
     }],
     [:password, {
       :placeholder => "Password for your account"
@@ -15,7 +15,7 @@ class IssueTrackers::GithubIssuesTracker < IssueTracker
 
   def check_params
     if Fields.detect {|f| self[f[0]].blank? }
-      errors.add :base, 'You must specify your Github repository, username and password'
+      errors.add :base, 'You must specify your GitHub repository, username and password'
     end
   end
 
@@ -25,7 +25,7 @@ class IssueTrackers::GithubIssuesTracker < IssueTracker
       issue = client.create_issue(project_id, issue_title(problem), body_template.result(binding).unpack('C*').pack('U*'), options = {})
       problem.update_attribute :issue_link, issue.html_url
     rescue Octokit::Unauthorized
-      raise IssueTrackers::AuthenticationError, "Could not authenticate with Github. Please check your username and password."
+      raise IssueTrackers::AuthenticationError, "Could not authenticate with GitHub. Please check your username and password."
     end
   end
 
diff --git a/app/views/users/show.html.haml b/app/views/users/show.html.haml
index 3c3eef6..b7a3d05 100644
--- a/app/views/users/show.html.haml
+++ b/app/views/users/show.html.haml
@@ -6,7 +6,6 @@
   = link_to 'destroy', user_path(@user), :method => :delete, :confirm => 'Seriously?', :class => 'button'
 
 
-
 %table.single_user
   %tr
     %th Email
diff --git a/config/config.example.yml b/config/config.example.yml
index 870b54e..3edbfaf 100644
--- a/config/config.example.yml
+++ b/config/config.example.yml
@@ -49,8 +49,8 @@ deployment:
   user: deploy
   deploy_to: /var/www/apps/errbit
 
-# Github OAuth configuration
-# If you want to allow authentication via Github, you will need to register
+# GitHub OAuth configuration
+# If you want to allow authentication via GitHub, you will need to register
 # your app at: https://github.com/settings/applications
 # If you hosted Errbit at errbit.example.com, you would fill in:
 #
diff --git a/spec/acceptance/acceptance_helper.rb b/spec/acceptance/acceptance_helper.rb
index 65f5be0..bbd8ba3 100644
--- a/spec/acceptance/acceptance_helper.rb
+++ b/spec/acceptance/acceptance_helper.rb
@@ -3,16 +3,17 @@ require 'capybara/rspec'
 
 OmniAuth.config.test_mode = true
 
-RSpec.configure do |config|
-  config.before(:each) do
-    OmniAuth.config.mock_auth[:github] = Hashie::Mash.new(
-      'provider' => 'github',
-      'uid' => '1763',
-      'extra' => {
-        'raw_info' => {
-          'login' => 'nashby'
-        }
+def mock_auth(user = "test_user", token = "abcdef")
+  OmniAuth.config.mock_auth[:github] = Hashie::Mash.new(
+    'provider' => 'github',
+    'uid' => '1763',
+    'extra' => {
+      'raw_info' => {
+        'login' => user
       }
-    )
-  end
+    },
+    'credentials' => {
+      'token' => token
+    }
+  )
 end
diff --git a/spec/acceptance/login_spec.rb b/spec/acceptance/login_spec.rb
deleted file mode 100644
index 10787a4..0000000
--- a/spec/acceptance/login_spec.rb
+++ /dev/null
@@ -1,14 +0,0 @@
-require 'acceptance/acceptance_helper'
-
-feature 'Log in' do
-  background do
-    Errbit::Config.stub(:github_authentication) { true }
-    Fabricate(:user, :github_login => 'nashby')
-  end
-
-  scenario 'log in via GitHub' do
-    visit '/'
-    click_link 'Sign in with GitHub'
-    page.should have_content 'Successfully authorized from Github account'
-  end
-end
diff --git a/spec/acceptance/sign_in_with_github_spec.rb b/spec/acceptance/sign_in_with_github_spec.rb
new file mode 100644
index 0000000..1ea54a6
--- /dev/null
+++ b/spec/acceptance/sign_in_with_github_spec.rb
@@ -0,0 +1,24 @@
+require 'acceptance/acceptance_helper'
+
+feature 'Sign in with GitHub' do
+  background do
+    Errbit::Config.stub(:github_authentication) { true }
+    Fabricate(:user, :github_login => 'nashby')
+  end
+
+  scenario 'log in via GitHub with recognized user' do
+    mock_auth('nashby')
+
+    visit '/'
+    click_link 'Sign in with GitHub'
+    page.should have_content 'Successfully authorized from GitHub account'
+  end
+
+  scenario 'reject unrecognized user if authenticating via GitHub' do
+    mock_auth('unknown_user')
+
+    visit '/'
+    click_link 'Sign in with GitHub'
+    page.should have_content 'There are no authorized users with GitHub login'
+  end
+end
diff --git a/spec/controllers/users/omniauth_callbacks_controller_spec.rb b/spec/controllers/users/omniauth_callbacks_controller_spec.rb
new file mode 100644
index 0000000..20c7d8d
--- /dev/null
+++ b/spec/controllers/users/omniauth_callbacks_controller_spec.rb
@@ -0,0 +1,42 @@
+require 'spec_helper'
+
+describe Users::OmniauthCallbacksController do
+
+  def stub_env_for_github_omniauth(login, token = nil)
+    # This a Devise specific thing for functional tests. See https://github.com/plataformatec/devise/issues/closed#issue/608
+    request.env["devise.mapping"] = Devise.mappings[:user]
+    env = {
+      "omniauth.auth" => Hashie::Mash.new(
+        :provider => 'github',
+        :extra => { :raw_info => { :login => login }},
+        :credentials => { :token => token }
+      )
+    }
+    @controller.stub!(:env).and_return(env)
+  end
+
+  context 'Linking a GitHub account to a signed in user' do
+    before do
+      sign_in @user = Fabricate(:user)
+    end
+
+    it "should show an error if another user already has that github login" do
+      Fabricate(:user, :github_login => "existing_user")
+      stub_env_for_github_omniauth("existing_user")
+      get :github
+
+      request.flash[:error].should include('already registered')
+      response.should redirect_to(user_path(@user))
+    end
+
+    it "should link an authorized GitHub account" do
+      stub_env_for_github_omniauth("new_user")
+      get :github
+
+      request.flash[:success].should include('Successfully linked')
+      response.should redirect_to(user_path(@user))
+    end
+  end
+
+  # See spec/acceptance/sign_in_with_github_spec.rb for 'Signing in with github' integration tests.
+end
diff --git a/spec/models/issue_trackers/github_issues_tracker_spec.rb b/spec/models/issue_trackers/github_issues_tracker_spec.rb
index fcd38f7..28a73c4 100644
--- a/spec/models/issue_trackers/github_issues_tracker_spec.rb
+++ b/spec/models/issue_trackers/github_issues_tracker_spec.rb
@@ -1,7 +1,7 @@
 require 'spec_helper'
 
 describe IssueTrackers::GithubIssuesTracker do
-  it "should create an issue on Github Issues with problem params, and set issue link for problem" do
+  it "should create an issue on GitHub Issues with problem params, and set issue link for problem" do
     notice = Fabricate :notice
     tracker = Fabricate :github_issues_tracker, :app => notice.app
     problem = notice.problem
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 4bbd6c7..a6104c5 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -27,3 +27,5 @@ RSpec.configure do |config|
   end
   config.include WebMock::API
 end
+
+OmniAuth.config.test_mode = true
diff --git a/spec/views/users/show.html.haml_spec.rb b/spec/views/users/show.html.haml_spec.rb
index 18e748a..d2e5cd4 100644
--- a/spec/views/users/show.html.haml_spec.rb
+++ b/spec/views/users/show.html.haml_spec.rb
@@ -5,11 +5,12 @@ describe 'users/show.html.haml' do
     user = stub_model(User, :created_at => Time.now)
   end
 
-  context 'with github auth' do
-    before do
-      Errbit::Config.stub(:github_authentication) { true }
-    end
+  before do
+    Errbit::Config.stub(:github_authentication) { true }
+    controller.stub(:current_user) { Fabricate(:user) }
+  end
 
+  context 'with GitHub authentication' do
     it 'shows github login' do
       user.github_login = 'test_user'
       assign :user, user
@@ -25,4 +26,35 @@ describe 'users/show.html.haml' do
       rendered.should_not match(/GitHub/)
     end
   end
+
+  context "Linking GitHub account" do
+    context 'viewing another user page' do
+      it "doesn't show and github linking buttons if user is not current user" do
+        assign :user, user
+        render
+        view.content_for(:action_bar).should_not include('Link GitHub account')
+        view.content_for(:action_bar).should_not include('Unlink GitHub account')
+      end
+    end
+
+    context 'viewing own user page' do
+      before do
+        @user = Fabricate(:user)
+        controller.stub!(:current_user).and_return(@user)
+        assign :user, @user
+      end
+
+      it 'shows link github button when no login or token' do
+        render
+        view.content_for(:action_bar).should include('Link GitHub account')
+      end
+
+      it 'shows unlink github button when login and token' do
+        @user.github_login = 'test_user'
+        @user.github_oauth_token = 'abcdef'
+        render
+        view.content_for(:action_bar).should include('Unlink GitHub account')
+      end
+    end
+  end
 end
--
libgit2 0.21.2