Log in a user from outside without having to fill a form

Hi all,

We're working on a project where is mandatory to "connect" an external db to the moodle's one.

I said connect but it isn't correct.

Sadly we don't have direct access to the external db.

The flow would be something like this

1. we contact an external page sending a token. the page respond with a json filled with the informations about the user associated with the token.
2. we insert it in moodle's db in some way
3. and we log it in

now the real problem is the last step because we'll have the username and an hashed psw.

if we wouldn't have the hash we could send an http post request to the default login page with the user's data.....

so, any Idea?

thnx in advance