Fix parsing of displayName

Currently, we only have one field for the name. The first part is
first name. The rest is last name. Obviously, this won't work in all
cases but is the best we can do for the moment.

src/oidc.js

@@ -648,17 +648,17 @@ async function claims(userId/*, use, scope*/) {
     if (error) return { error: 'user not found' };
 
     const displayName = user.displayName || user.username || ''; // displayName can be empty and username can be null
-    const nameParts = displayName.split(' ');
-    const firstName = nameParts[0];
-    const lastName = nameParts.length > 1  ? nameParts[nameParts.length - 1] : ''; // choose last part, if it exists
+    const { firstName, lastName, middleName } = users.parseDisplayName(displayName);
 
     const { fqdn:dashboardFqdn } = await dashboard.getLocation();
 
+    // https://openid.net/specs/openid-connect-core-1_0.html#StandardClaims
     const claims = {
         sub: user.username, // it is essential to always return a sub claim
         email: user.email,
         email_verified: true,
         family_name: lastName,
+        middle_name: middleName,
         given_name: firstName,
         locale: 'en-US',
         name: user.displayName,