Firstly, please consider if people he will have any idea what "ERP" is? I had to look it up
Assuming it's just a database of some sort, you should have a look at the external database authentication plugin, see External_database_authentication.
The problem you might have is that the plugin requires the data to be in a single table in a simple format. If your data doesn't match up you could (for example) arrange a nightly export to a new database/table in a more appropriate format.