Fix false login state on OAuth signup page

Having a `Username` field populated in the page data tells the base
template to display navigation that only a logged in user should see. So
this renames the field to `LoginUsername`, similar to our login.tmpl
page.

Ref T712

oauth_signup.go

@@ -29,9 +29,9 @@ type viewOauthSignupVars struct {
 	ClientID        string
 	TokenHash       string
 
-	Username string
-	Alias    string
-	Email    string
+	LoginUsername string
+	Alias         string
+	Email         string
 }
 
 const (
@@ -184,9 +184,9 @@ func (h oauthHandler) showOauthSignupPage(app *App, w http.ResponseWriter, r *ht
 		ClientID:        tp.ClientID,
 		TokenHash:       tp.TokenHash,
 
-		Username: username,
-		Alias:    alias,
-		Email:    email,
+		LoginUsername: username,
+		Alias:         collTitle,
+		Email:         email,
 	}
 
 	// Display any error messages

pages/signup-oauth.tmpl

@@ -85,7 +85,7 @@ form dd {
                 <label>
                     <dt>Username</dt>
 					<dd>
-		<input type="text" id="username" name="username" style="width: 100%; box-sizing: border-box;" placeholder="Username" value="{{.Username}}" /><br />
+		<input type="text" id="username" name="username" style="width: 100%; box-sizing: border-box;" placeholder="Username" value="{{.LoginUsername}}" /><br />
 		{{if .Federation}}<p id="alias-site" class="demo">@<strong>your-username</strong>@{{.FriendlyHost}}</p>{{else}}<p id="alias-site" class="demo">{{.FriendlyHost}}/<strong>your-username</strong></p>{{end}}
                     </dd>
                 </label>