Monitoring attributes per IdP

We would like to keep records of which attributes are given out per IdP. So we would like to get an overview like this:

- idp: https://entityid.example.com/
  num_authentications: 1200
  attributes:
    - uid: 1199
    - schacHomeOrg: 1200
    - displayName: 1167
    - mail: 999
    - edupersonAffiliation: 321
    - isMemberOf: 2

meaning that that total number of authentication from this service was 1200, all authentications had schacHome in the assertion, 1 was missing a uid (which caused an error, obviously), 999 had a mail address, etc.

Note that we thus not only want to count successful logins, but also errors (as long a valid assertion was received).

I don't think that EB needs to aggregate the statistics to the form as specified here; logging a proper line per login that can be processed offline probably suffices.