When refreshing the token, look up the user in a way that doesn't suffer

from #1586

Expose a means of looking up a user by identity and server to avoid
problems if the same user identity exists for multiple servers, which
can happen when connecting to the same server via different hostnames.

lib/user-methods.js

@@ -91,7 +91,7 @@ function refreshAccessToken(user, localRealmPath, realmUrl) {
             // Look up a fresh instance of the user.
             // We do this because in React Native Remote Debugging
             // `Realm.clearTestState()` will have invalidated the user object
-            let newUser = user.constructor.all[user.identity];
+            let newUser = user.constructor._getExistingUser(user.server, user.identity);
             if (!newUser) {
                 return;
             }

src/js_sync.hpp

@@ -59,6 +59,7 @@ class UserClass : public ClassDefinition<T, SharedUser> {
     using Value = js::Value<T>;
     using Function = js::Function<T>;
     using ReturnValue = js::ReturnValue<T>;
+    using Arguments = js::Arguments<T>;
 
 public:
     std::string const name = "User";
@@ -79,10 +80,12 @@ public:
 
     static void create_user(ContextType, FunctionType, ObjectType, size_t, const ValueType[], ReturnValue &);
     static void admin_user(ContextType, FunctionType, ObjectType, size_t, const ValueType[], ReturnValue &);
+    static void get_existing_user(ContextType, ObjectType, Arguments, ReturnValue&);
 
     MethodMap<T> const static_methods = {
         {"createUser", wrap<create_user>},
-        {"_adminUser", wrap<admin_user>}
+        {"_adminUser", wrap<admin_user>},
+        {"_getExistingUser", wrap<get_existing_user>},
     };
 
     /*static void current_user(ContextType ctx, ObjectType object, ReturnValue &return_value);*/
@@ -153,6 +156,18 @@ void UserClass<T>::admin_user(ContextType ctx, FunctionType, ObjectType this_obj
     return_value.set(create_object<T, UserClass<T>>(ctx, user));
 }
 
+template<typename T>
+void UserClass<T>::get_existing_user(ContextType ctx, ObjectType, Arguments arguments, ReturnValue& return_value) {
+    arguments.validate_count(2);
+    SharedUser *user = new SharedUser(syncManagerShared().get_existing_logged_in_user(
+        SyncUserIdentifier{
+            Value::validated_to_string(ctx, arguments[1], "identity"),
+            Value::validated_to_string(ctx, arguments[0], "authServerUrl"),
+        }
+    ));
+    return_value.set(create_object<T, UserClass<T>>(ctx, user));
+}
+
 template<typename T>
 void UserClass<T>::all_users(ContextType ctx, ObjectType object, ReturnValue &return_value) {
     auto users = Object::create_empty(ctx);