SAML channel adding does not support a multi-value "channels" claim

[tlskinneriv]

Description:

When a user is added via SAML login, multiple values in the "channels" claim results in no channel subscriptions for the user. A single field in the "channels" claim containing a comma-separated list of channels works correctly.

Steps to reproduce:

1. Setup a SAML connetion with an IdP to pass "channels" claim with multiple values (in my scenario specifically, Microsoft ADFS with multiple group memberships passed as claims with the claim values set to the desired channel name for the user's AD groups)
2. Login with a previously unregistered user.

Expected behavior:

User is subscribed to the specified channels.

Actual behavior:

If "channels" is set to a single value in the claim, then works as expected. If multiple values are passed in the "channels" claim, user is not subscribed to any of the specified channels.

Server Setup Information:

• Version of Rocket.Chat Server: 2.2.0
• Operating System: RHEL 7
• Deployment Method: Office Docker Rocket.Chat 2.2.0 container, Official Docker Mongo 4.0 container
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version:
• MongoDB Version: 4.0

Client Setup Information

• Desktop App or Browser Version: Chrome
• Operating System: Windows 10

Additional context

Fix can be implemented in /app/meteor-accounts-saml/server/saml_server.js to support both single claim value comma-separated list and multi-value claim. I am submitting a PR with the fix code in it.

Relevant logs: