[Openid-specs-mobile-profile] How to generate the "sub" in Mobile Connect

[GONZALO FERNANDEZ RODRIGUEZ]

Hi Guys,

I will not be able to attend to our call tomorrow, however I would like to add this topic to the tomorrow's call in order to be discussed (Jorg is aware of it, because it is an action point from our calls in the GSMA Working Group).

As all we know, the MSISDN is something susceptible to be ported from an operator to another, and this can have a big impact in the Service Providers that already have a "sub" to recognise the owner of this MSISDN.
In the GSMA Working Group we are talking about the need to migrate the sub (aka PCR: Pseudonymous Customer Reference) in case of portability. To do that, we need that the PCR is not tied to the MSISDN but to a Mobile Connect identifier that must be unique across all the operators.

As per the OpenID Connect spec, the Service Providers should check the pair iss+sub to identify the users, however this wouldn't be possible in Mobile Connect, because we aim to identify the same user irrrespective of which is the current Identity Provider which the user belongs to. The conclusion is that we need to generates PCR with the follow constraints:


  1.  The PCR must be unique across all the operators.
  2.  The PCR should be created only once per MSISDN and to maintain it all the portabilities long.
     *   To achieve that, one possibility could be to have a central database, however this could be a poor solution due to scalability and additional integrations between the OIDC providers and this common database.
     *   Another possibility could be that PCR's are created by the MNO where the user is registered in the Mobile Connect for the first time. As this solution implies to create the PCR in a distributed way, it need to agree how to do it in order to avoid collisions, so we have proposed the next mechanism to create this PCR's:
        *   Generate a PCR like: Hash(iss+client_id+user_id)
        *   The user_id would be up to each operator
        *   The client_id (Service Provider identifier) should be agreed among all the operators, because it would be necessary when the user is ported to know which PCR is related with which Service Provider.
        *   The iss avoid collisions among operators
        *   The Hash is something to obfuscate
  3.  This PCR should be deleted in the event that the MSISDN is recycled.

It would be very useful to have comments on this working group, so I would encourage you to discuss this topic to give feedback to the GSMA WG.

Thanks in advance, and sorry to not be able to attend the call tomorrow.
Gonza.

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