Site <> Forum each on a different server..

[Digma]

Currently looking at a situation where I am more or less forced to create the following setup (due to contracts for the hosting of the msg board)

Setup:
1 server at hosting company A which contains the msg board with the database.

1 server at hosting company B which contains the website itself with no database.

Question:
How can I make it so that people can login to the website with the same information they use for the msg board, without having to copy the database.

Summarized:
Visitor logs in on server at hosting company A using login info from server at hosting company B and remains on server at hosting company A.

Hope it makes sense and if someone can point me into the right direction.

Thank you in advance.