Creating a SQL Login and User on an AlwaysOn Replica I have a database (DB1) which is synced to (DB2) on another server (via AlwaysOn - SQL Server 2014). 

I want to give a user read access to DB2. I create a SQL login and database user in DB1. The new database user is migrated to DB2, but the SQL login is not (which makes sense). 

The problem is that when I attempt to create a SQL login for the user on DB2 and give the user read rights to DB2, tied to the user account that came from DB1, I get an error saying DB2 is read only and cannot be modified. 

So, how can I accomplish this?
You need to create the login on the DB2 server. Use Robert's script so that it grabs the sid and password, well if it's a SQL account that is. 

Then grant the permission on DB1. That permission will auto-magically get copied over to DB2 due to the AG. 

There is no way to just grant permission on DB2. It has to be done on DB1. You can control access by disabling the login on DB1 though.