Update signup-via-invite page

This updates signup.tmpl to include all supported OAuth methods and respect the new `DisablePasswordAuth` config value.

invites.go

@@ -170,14 +170,14 @@ func handleViewInvite(app *App, w http.ResponseWriter, r *http.Request) error {
 
 	p := struct {
 		page.StaticPage
+		*OAuthButtons
 		Error   string
 		Flashes []template.HTML
 		Invite  string
-		OAuth   *OAuthButtons
 	}{
 		StaticPage:   pageForReq(app, r),
+		OAuthButtons: NewOAuthButtons(app.cfg),
 		Invite:       inviteCode,
-		OAuth:      NewOAuthButtons(app.cfg),
 	}
 
 	if expired {

pages/signup.tmpl

@@ -70,25 +70,9 @@ form dd {
 		</ul>{{end}}
 
 		<div id="billing">
-			{{ if or .OAuth.SlackEnabled .OAuth.WriteAsEnabled .OAuth.GitLabEnabled }}
-				<div class="row content-container signinbtns">
-					{{ if .OAuth.SlackEnabled }}
-						<a class="loginbtn" href="/oauth/slack{{if .Invite}}?invite_code={{.Invite}}{{end}}"><img alt="Sign in with Slack" height="40" width="172" src="/img/sign_in_with_slack.png" srcset="/img/sign_in_with_slack.png 1x, /img/sign_in_with_slack@2x.png 2x" /></a>
-					{{ end }}
-					{{ if .OAuth.WriteAsEnabled }}
-						<a class="btn cta loginbtn" id="writeas-login" href="/oauth/write.as{{if .Invite}}?invite_code={{.Invite}}{{end}}">Sign in with <strong>Write.as</strong></a>
-					{{ end }}
-					{{ if .OAuth.GitLabEnabled }}
-						<a class="btn cta loginbtn" id="gitlab-login" href="/oauth/gitlab{{if .Invite}}?invite_code={{.Invite}}{{end}}">Sign in with <strong>{{.OAuth.GitLabDisplayName}}</strong></a>
-					{{ end }}
-				</div>
-
-				<div class="or">
-					<p>or</p>
-					<hr class="short" />
-				</div>
-			{{ end }}
+			{{template "oauth-buttons" .}}
 
+			{{if not .DisablePasswordAuth}}
 			<form action="/auth/signup" method="POST" id="signup-form" onsubmit="return signup()">
 				<input type="hidden" name="invite_code" value="{{.Invite}}" />
 				<dl class="billing">
@@ -112,6 +96,7 @@ form dd {
 					</dt>
 				</dl>
 			</form>
+			{{end}}
 		</div>
 		{{ end }}
 	</div>