Implement MSC4098: SCIM provisioning

[azmeuk]

This is an implementation of MSC4098.
It implements a subset of the SCIM provisioning protocol.

Implementation largely takes inspiration (and shameless copied) from synapse/rest/admin/users.py.

What's implemented:

• The main endpoints:
  • /Users (GET, POST)
  • /Users/<user_id> (GET, PUT, DELETE)
  • /ServiceProviderConfig (GET)
  • /Schemas (GET)
  • /Schemas/<schema_id> (GET)
  • /ResourceTypes (GET)
  • /ResourceTypes/<resource_type_id>
• pagination
• The user attributes:
  • userName
  • password
  • emails
  • phoneNumbers
  • displayName
  • photos (as a MXC URI)
  • active

What is defined in the SCIM specs but not implemented here:

• A few endpoints:
  • /Users (PATCH)
  • /Me (GET, POST, PUT, PATCH, DELETE)
  • /Groups (GET, POST, PUT, PATCH) (but this no relevant)
  • /Bulk (POST)
  • /.search (POST)
• filtering
• sorting
• attributes selection
• ETags

It currently lacks a few tests and some documentation. I wanted to open this PR to check wether I am going in the good direction.

What do you think?

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Code style is correct
  (run the linters)

[erikjohnston]

(I've taken this out of the review queue as its in draft, let us know if you want feedback)

[azmeuk]

Hi @erikjohnston
Thank you for your feedback offering. Indeed this is a draft, but I hope to take back the development soon.

There is one design question though. I see that there is a dependency to pydantic in synapse, and I recently published scim2-models that is a library that helps to parse and serialize SCIM2 payloads using pydantic. I think the SCIM implementation would greatly benefit from using scim2-models, as a big part of the specification compliance would be delegated to the library.

Would it be acceptable to add a dependency towards scim2-models in synapse, or should I continue checking and building SCIM2 payloads manually?