You would want Xenforo to handle any writes. Reading and authenticating against is easily okay. While there is no API built in at the moment there are addon's for either REST support or another API setup and that should probably help out.
It would likely be best. Not saying it's the only way. But given certain issues that are likely to crop up its best to have one or the other handling user data writes. You can look at other SSO systems for Xenforo as an example.
It's different than integrating other software. I guess off the top of my head the closest thing in Xenforo that can create user accounts, etc. Is Tapatalk. I mean really the app talks to the plugin talks to xenforo. While it's not well coded thats another example for you to look at.
Depending on what you want I imagine you just need someone to create a plugin that provides an interface for your app to login, create user accounts, share data between the platforms. But your needs are better known by you.
A database is a database is a database. Doesn't matter what application is using it, creating the accounts, profiles, etc. As long as the information that is in the database aligns with what is needed by each application, it really doesn't matter.
If you want to use your app to write to the database, that's fine, just make sure all the information is there that xF needs (and in the proper format), or you're likely to run into problems, errors, etc.
If you want to use your app to write to the database, that's fine, just make sure all the information is there that xF needs (and in the proper format), or you're likely to run into problems, errors, etc.
