More secured auth token - some signature on request

[jstuczyn]

Currently the service provider gives out authentication tokens to everyone. If you forgot yours - it just gives you back what you should have had (so anyone could learn your token this way);
The request would need some signature to ensure that the provider is talking with the right client.

[aniampio]

Right now in the code, we allow a particular client to register only once, so we avoid this isse partially. Anyway, we can implement a signature schema, just to allow people get there authentication token again if they forget.