Oauth2 consumer (#679)

* initial stuff for oauth2 login, fails on:
* login button on the signIn page to start the OAuth2 flow and a callback for each provider
Only GitHub is implemented for now
* show login button only when the OAuth2 consumer is configured (and activated)
* create macaron group for oauth2 urls
* prevent net/http in modules (other then oauth2)
* use a new data sessions oauth2 folder for storing the oauth2 session data
* add missing 2FA when this is enabled on the user
* add password option for OAuth2 user , for use with git over http and login to the GUI
* add tip for registering a GitHub OAuth application
* at startup of Gitea register all configured providers and also on adding/deleting of new providers
* custom handling of errors in oauth2 request init + show better tip
* add ExternalLoginUser model and migration script to add it to database
* link a external account to an existing account (still need to handle wrong login and signup) and remove if user is removed
* remove the linked external account from the user his settings
* if user is unknown we allow him to register a new account or link it to some existing account
* sign up with button on signin page (als change OAuth2Provider structure so we can store basic stuff about providers)

* from gorilla/sessions docs:
"Important Note: If you aren't using gorilla/mux, you need to wrap your handlers with context.ClearHandler as or else you will leak memory!"
(we're using gorilla/sessions for storing oauth2 sessions)

* use updated goth lib that now supports getting the OAuth2 user if the AccessToken is still valid instead of re-authenticating (prevent flooding the OAuth2 provider)

5 files changed, 131 insertions, 96 deletions

diff --git a/templates/user/auth/link_account.tmpl b/templates/user/auth/link_account.tmpl
new file mode 100644
index 0000000000..5dc54ca5a4
--- /dev/null
+++ b/templates/user/auth/link_account.tmpl
@@ -0,0 +1,13 @@
+{{template "base/head" .}}
+<div class="user link-account">
+	<div class="ui middle very relaxed page grid">
+		<div class="column">
+			<p class="large center">
+				{{.i18n.Tr "link_account_signin_or_signup"}}
+			</p>
+		</div>
+	</div>
+</div>
+{{template "user/auth/signin_inner" .}}
+{{template "user/auth/signup_inner" .}}
+{{template "base/footer" .}}
diff --git a/templates/user/auth/signin.tmpl b/templates/user/auth/signin.tmpl
index 85b7e70277..5ed8612e3f 100644
--- a/templates/user/auth/signin.tmpl
+++ b/templates/user/auth/signin.tmpl
@@ -1,44 +1,3 @@
 {{template "base/head" .}}
-<div class="user signin">
-	<div class="ui middle very relaxed page grid">
-		<div class="column">
-			<form class="ui form" action="{{.Link}}" method="post">
-				{{.CsrfTokenHtml}}
-				<h3 class="ui top attached header">
-					{{.i18n.Tr "sign_in"}}
-				</h3>
-				<div class="ui attached segment">
-					{{template "base/alert" .}}
-					<div class="required inline field {{if .Err_UserName}}error{{end}}">
-						<label for="user_name">{{.i18n.Tr "home.uname_holder"}}</label>
-						<input id="user_name" name="user_name" value="{{.user_name}}" autofocus required>
-					</div>
-					<div class="required inline field {{if .Err_Password}}error{{end}}">
-						<label for="password">{{.i18n.Tr "password"}}</label>
-						<input id="password" name="password" type="password" value="{{.password}}" autocomplete="off" required>
-					</div>
-					<div class="inline field">
-						<label></label>
-						<div class="ui checkbox">
-							<label>{{.i18n.Tr "auth.remember_me"}}</label>
-							<input name="remember" type="checkbox">
-						</div>
-					</div>
-
-					<div class="inline field">
-						<label></label>
-						<button class="ui green button">{{.i18n.Tr "sign_in"}}</button>
-						<a href="{{AppSubUrl}}/user/forget_password">{{.i18n.Tr "auth.forget_password"}}</a>
-					</div>
-					{{if .ShowRegistrationButton}}
-						<div class="inline field">
-							<label></label>
-							<a href="{{AppSubUrl}}/user/sign_up">{{.i18n.Tr "auth.sign_up_now" | Str2html}}</a>
-						</div>
-					{{end}}
-				</div>
-			</form>
-		</div>
-	</div>
-</div>
+{{template "user/auth/signin_inner" .}}
 {{template "base/footer" .}}
diff --git a/templates/user/auth/signin_inner.tmpl b/templates/user/auth/signin_inner.tmpl
new file mode 100644
index 0000000000..34fcea08fc
--- /dev/null
+++ b/templates/user/auth/signin_inner.tmpl
@@ -0,0 +1,57 @@
+<div class="user signin{{if .LinkAccountMode}} icon{{end}}">
+	<div class="ui middle very relaxed page grid">
+		<div class="column">
+			<form class="ui form" action="{{if not .LinkAccountMode}}{{.Link}}{{else}}{{.SignInLink}}{{end}}" method="post">
+				{{.CsrfTokenHtml}}
+				<h3 class="ui top attached header">
+					{{.i18n.Tr "sign_in"}}
+				</h3>
+				<div class="ui attached segment">
+					{{if or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeSignIn)}}
+					{{template "base/alert" .}}
+					{{end}}
+					<div class="required inline field {{if and (.Err_UserName) (or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeSignIn))}}error{{end}}">
+						<label for="user_name">{{.i18n.Tr "home.uname_holder"}}</label>
+						<input id="user_name" name="user_name" value="{{.user_name}}" autofocus required>
+					</div>
+					<div class="required inline field {{if and (.Err_Password) (or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeSignIn))}}error{{end}}">
+						<label for="password">{{.i18n.Tr "password"}}</label>
+						<input id="password" name="password" type="password" value="{{.password}}" autocomplete="off" required>
+					</div>
+					{{if not .LinkAccountMode}}
+					<div class="inline field">
+						<label></label>
+						<div class="ui checkbox">
+							<label>{{.i18n.Tr "auth.remember_me"}}</label>
+							<input name="remember" type="checkbox">
+						</div>
+					</div>
+					{{end}}
+
+					<div class="inline field">
+						<label></label>
+						<button class="ui green button">{{.i18n.Tr "sign_in"}}</button>
+						<a href="{{AppSubUrl}}/user/forget_password">{{.i18n.Tr "auth.forget_password"}}</a>
+					</div>
+
+					{{if .ShowRegistrationButton}}
+						<div class="inline field">
+							<label></label>
+							<a href="{{AppSubUrl}}/user/sign_up">{{.i18n.Tr "auth.sign_up_now" | Str2html}}</a>
+						</div>
+					{{end}}
+
+					{{if .OAuth2Providers}}
+					<div class="ui attached segment">
+						<div class="oauth2 center">
+							<div>
+								<p>{{.i18n.Tr "sign_in_with"}}</p>{{range $key, $value := .OAuth2Providers}}<a href="{{AppSubUrl}}/user/oauth2/{{$key}}"><img alt="{{$value.DisplayName}}" title="{{$value.DisplayName}}" src="{{AppSubUrl}}{{$value.Image}}"></a>{{end}}
+							</div>
+						</div>
+					</div>
+					{{end}}
+				</div>
+			</form>
+		</div>
+	</div>
+</div>
\ No newline at end of file
diff --git a/templates/user/auth/signup.tmpl b/templates/user/auth/signup.tmpl
index aeae4f957e..b814b466c8 100644
--- a/templates/user/auth/signup.tmpl
+++ b/templates/user/auth/signup.tmpl
@@ -1,56 +1,3 @@
 {{template "base/head" .}}
-<div class="user signup">
-	<div class="ui middle very relaxed page grid">
-		<div class="column">
-			<form class="ui form" action="{{.Link}}" method="post">
-				{{.CsrfTokenHtml}}
-				<h3 class="ui top attached header">
-					{{if .IsSocialLogin}}{{.i18n.Tr "social_sign_in" | Str2html}}{{else}}{{.i18n.Tr "sign_up"}}{{end}}
-				</h3>
-				<div class="ui attached segment">
-					{{template "base/alert" .}}
-					{{if .DisableRegistration}}
-						<p>{{.i18n.Tr "auth.disable_register_prompt"}}</p>
-					{{else}}
-						<div class="required inline field {{if .Err_UserName}}error{{end}}">
-							<label for="user_name">{{.i18n.Tr "username"}}</label>
-							<input id="user_name" name="user_name" value="{{.user_name}}" autofocus required>
-						</div>
-						<div class="required inline field {{if .Err_Email}}error{{end}}">
-							<label for="email">{{.i18n.Tr "email"}}</label>
-							<input id="email" name="email" type="email" value="{{.email}}" required>
-						</div>
-						<div class="required inline field {{if .Err_Password}}error{{end}}">
-							<label for="password">{{.i18n.Tr "password"}}</label>
-							<input id="password" name="password" type="password" value="{{.password}}" autocomplete="off" required>
-						</div>
-						<div class="required inline field {{if .Err_Password}}error{{end}}">
-							<label for="retype">{{.i18n.Tr "re_type"}}</label>
-							<input id="retype" name="retype" type="password" value="{{.retype}}" autocomplete="off" required>
-						</div>
-						{{if .EnableCaptcha}}
-							<div class="inline field">
-								<label></label>
-								{{.Captcha.CreateHtml}}
-							</div>
-							<div class="required inline field {{if .Err_Captcha}}error{{end}}">
-								<label for="captcha">{{.i18n.Tr "captcha"}}</label>
-								<input id="captcha" name="captcha" value="{{.captcha}}" autocomplete="off">
-							</div>
-						{{end}}
-
-						<div class="inline field">
-							<label></label>
-							<button class="ui green button">{{.i18n.Tr "auth.create_new_account"}}</button>
-						</div>
-						<div class="inline field">
-							<label></label>
-							<a href="{{AppSubUrl}}/user/login">{{if .IsSocialLogin}}{{.i18n.Tr "auth.social_register_helper_msg"}}{{else}}{{.i18n.Tr "auth.register_helper_msg"}}{{end}}</a>
-						</div>
-					{{end}}
-				</div>
-			</form>
-		</div>
-	</div>
-</div>
+{{template "user/auth/signup_inner" .}}
 {{template "base/footer" .}}
diff --git a/templates/user/auth/signup_inner.tmpl b/templates/user/auth/signup_inner.tmpl
new file mode 100644
index 0000000000..869f3d5342
--- /dev/null
+++ b/templates/user/auth/signup_inner.tmpl
@@ -0,0 +1,59 @@
+<div class="user signup{{if .LinkAccountMode}} icon{{end}}">
+	<div class="ui middle very relaxed page grid">
+		<div class="column">
+			<form class="ui form" action="{{if not .LinkAccountMode}}{{.Link}}{{else}}{{.SignUpLink}}{{end}}" method="post">
+				{{.CsrfTokenHtml}}
+				<h3 class="ui top attached header">
+					{{.i18n.Tr "sign_up"}}
+				</h3>
+				<div class="ui attached segment">
+					{{if or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeRegister)}}
+					{{template "base/alert" .}}
+					{{end}}
+					{{if .DisableRegistration}}
+						<p>{{.i18n.Tr "auth.disable_register_prompt"}}</p>
+					{{else}}
+						<div class="required inline field {{if and (.Err_UserName) (or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeRegister))}}error{{end}}">
+							<label for="user_name">{{.i18n.Tr "username"}}</label>
+							<input id="user_name" name="user_name" value="{{.user_name}}" autofocus required>
+						</div>
+						<div class="required inline field {{if .Err_Email}}error{{end}}">
+							<label for="email">{{.i18n.Tr "email"}}</label>
+							<input id="email" name="email" type="email" value="{{.email}}" required>
+						</div>
+						<div class="required inline field {{if and (.Err_Password) (or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeRegister))}}error{{end}}">
+							<label for="password">{{.i18n.Tr "password"}}</label>
+							<input id="password" name="password" type="password" value="{{.password}}" autocomplete="off" required>
+						</div>
+						<div class="required inline field {{if and (.Err_Password) (or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeRegister))}}error{{end}}">
+							<label for="retype">{{.i18n.Tr "re_type"}}</label>
+							<input id="retype" name="retype" type="password" value="{{.retype}}" autocomplete="off" required>
+						</div>
+						{{if .EnableCaptcha}}
+							<div class="inline field">
+								<label></label>
+								{{.Captcha.CreateHtml}}
+							</div>
+							<div class="required inline field {{if .Err_Captcha}}error{{end}}">
+								<label for="captcha">{{.i18n.Tr "captcha"}}</label>
+								<input id="captcha" name="captcha" value="{{.captcha}}" autocomplete="off">
+							</div>
+						{{end}}
+
+						<div class="inline field">
+							<label></label>
+							<button class="ui green button">{{.i18n.Tr "auth.create_new_account"}}</button>
+						</div>
+
+						{{if not .LinkAccountMode}}
+						<div class="inline field">
+							<label></label>
+							<a href="{{AppSubUrl}}/user/login">{{.i18n.Tr "auth.register_helper_msg"}}</a>
+						</div>
+						{{end}}
+					{{end}}
+				</div>
+			</form>
+		</div>
+	</div>
+</div>
\ No newline at end of file