Fix, add user agent to OAuth flow network calls.

lib/models/auth/oauth_credentials.dart

@@ -111,6 +111,7 @@ class OAuthCredentials implements ICredentials {
     final idEndpoint = Uri.parse('https://$serverName/api/v1/apps');
 
     final request = NetworkRequest(idEndpoint,
+        headers: ref.read(userAgentHeaderProvider),
         body: {
           'client_name': 'Relatica',
           'redirect_uris': redirectUrl,
@@ -180,13 +181,15 @@ class OAuthCredentials implements ICredentials {
         );
       }
       final url2 = Uri.parse('https://$serverName/oauth/token');
-      final request = NetworkRequest(url2, body: {
-        'client_id': clientId,
-        'client_secret': clientSecret,
-        'redirect_uri': redirectUrl,
-        'grant_type': 'authorization_code',
-        'code': code,
-      });
+      final request = NetworkRequest(url2,
+          headers: ref.read(userAgentHeaderProvider),
+          body: {
+            'client_id': clientId,
+            'client_secret': clientSecret,
+            'redirect_uri': redirectUrl,
+            'grant_type': 'authorization_code',
+            'code': code,
+          });
       final response = await ref.read(httpPostProvider(request).future);
       response.match(onSuccess: (body) {
         ref