SAML username mapping is not working

Description:

When username is mapped to a SAML field, it is ignored, and another username is created, not even related to a SAML field.

Steps to reproduce:

1. Configure SAML mapping for username:
   {"username":"urn:oid:1-2-840-113556-1-4-656", "name":"urn:oid:2-5-4-31", "email":"urn:oid:0-9-2342-19200300-100-1-3"}

2. Connect user with SSO and check RocketChat behavior (full logs below)

Expected behavior:

username should be the value selected in the mapping

Actual behavior:

username is configured I don't know how, it's name.firstname but it must be constructed in some way, since it does not appear in the SAML response, not even in the email.

Server Setup Information:

• Version of Rocket.Chat Server: 3.10.3
• Operating System: Ubuntu
• Deployment Method: Helm chart
• Number of Running Instances: 1
• MongoDB Version: 4.0.3

Some SAML settings:

• Generate username: true (if not set, RocketChat asks the user to define his username, by default being doe.john)
• Normalize username : No normalization
• Immutable fieldname: username
• Overwrite user fullname (use idp attribute): true
• Overwrite user mail (use idp attribute): true

Relevant logs:

Field mapping is the following, so username should be mapped to urn:oid:1-2-840-113556-1-4-656

{"username":"urn:oid:1-2-840-113556-1-4-656", "name":"urn:oid:2-5-4-31", "email":"urn:oid:0-9-2342-19200300-100-1-3"}

At creation time, SAML response includes correct fields. urn:oid:1-2-840-113556-1-4-656 is MRJD27

I20210126-16:42:08.533(0) server.js:204 steffo:meteor-accounts-saml ➔ info RESULT :{"profile":{"inResponseToId":"id-anPnRnxMTfjyu8TD3","issuer":"https://sign-on.my-domain.com/idp/shibboleth","nameID":"john.doe@my-domain.com","nameIDFormat":"urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress","sessionIndex":"_d3b8257597316a4faf8e95b5172bc5b9","mail":"john.doe@my-domain.com","email":"john.doe@my-domain.com","urn:oid:0-0-10-15":"USER","urn:oid:1-2-840-113556-1-4-656":"MRJD27","urn:oid:2-5-4-31":"DOE John","urn:oid:2-5-4-4":"Doe","urn:oid:2-5-4-42":"John","urn:oid:0-9-2342-19200300-100-1-3":"john.doe@my-domain.com"}} 

Mapping is checked by RC, everything is fine

I20210126-16:42:08.534(0) server.js:204 steffo:meteor-accounts-saml ➔ info parsed userDataMap {   customFields: Map {},   attributeList: Set {     'urn:oid:1-2-840-113556-1-4-656',     'urn:oid:2-5-4-31',     'urn:oid:0-9-2342-19200300-100-1-3'   },   email: { fieldName: 'urn:oid:0-9-2342-19200300-100-1-3' },   username: { fieldName: 'urn:oid:1-2-840-113556-1-4-656' },   name: { fieldName: 'urn:oid:2-5-4-31' },   identifier: { type: 'username' } }

Then user is created, but username is not the expected value.

I20210126-16:42:08.558(0) server.js:204 Integrations ➔ Outgoing WebHook.debug Got the event arguments for the event: userCreated {   event: 'userCreated',   user: {     _id: 'ZQhvmhu8rY4HLn9pm',     createdAt: 2021-01-26T16:42:08.539Z,     name: 'DOE John',     active: true,     emails: [ [Object] ],     services: { saml: [Object] },     username: 'doe.john',     type: 'user',     status: 'offline',     _updatedAt: 2021-01-26T16:42:08.539Z   } }