Access Rights To Two Mssql Dbs Via Password Protected Role

I dont know how to arrange situation when application enduser needs to access data in two databases of mssql server concurently in those circumstances that access rights to the data should be restricted by password protected role (whose password is not known to the end user).

Detailed description of problem:

So far there was an application, that manipulated its data, saved in mssql server's database. End user authenticates to application by his (mssql server's) login name and password. The application authenticates the user by connecting to the database with the given name/password credentials, and then the application sets application role with hardcoded name/password. Thus application role sets the access rights for consequent end user's requests, delivered via application to the database server.

The goal is that end user cannot manipulate application database data when connects to the database by other means (e. g. via SQL server Manager), because he does not know the application role's password.

Now suppose that there are two applications (A1, A2), both using the same model for access restrictions. Each of them has its own database (A1DB, A2DB) and its own application role (A1R residing in A1DB, A2R residing in A2DB). End user (login) X can manipulate A1DB data when connects via A1, and A2DB data when connects via A2, and NO data when connects by other means.

Finally suppose that some subset of A2 data (let's say one table) is useful to see also via A1 application. There is no problem to add to A1DB view, that shows data from A2DB table together with A1DB tables. But when the user is connected via A1, he cannot see the data, because query on A1 view fails (user has not access rights on A2 data).

The access rights for A1 enduser cannot be set by no means i know because:

1) I cannot set the rights via public (guest) access because in that case they will be accessible to any users connected by any third party products, which is supposed to be security hole.

2) I cannot set the rights via dbuser or dbrole privileges, because they will not work when connected via A1 application (setting the app role suppresses the db privileges)

3) I cannot set the rights via application role because two application roles cannot be set concurrently.

4) I cannot abandon using application roles mechanism and use database roles mechanism, because db roles cannot be protected by independent password (not known to the enduser).

Please can anybody review my problem and either find the mistake in my approach, or propose other solution? So far I suppose the problem is my ignorance, because I am not great mssql expert.