Summary

Change the return of mongoc_uri_get_auth_source to return "$external" for MONGODB-AWS to agree with the applied auth source.

Background & Motivation

Tests for the MONGODB-AWS auth mechanism were added in SPEC-1515 but missed when implementing MONGODB-AWS.

Many MONGODB-AWS connection string tests fail. Example:

{
  "description": "should recognise the mechanism (MONGODB-AWS)",
  "uri": "mongodb://localhost/?authMechanism=MONGODB-AWS",
  "valid": true,
  "credential": {
    "username": null,
    "password": null,
    "source": "$external",
    "mechanism": "MONGODB-AWS",
    "mechanism_properties": null
  }
}

The expected "source" is "$external" to agree with the specified default:

source

MUST be "$external". Defaults to $external.

However, mongoc_uri_get_auth_source returns "admin". Internally, "$external" is hardcoded for MONGODB-AWS auth. As a workaround, this test is planned to be skipped (search code for this ticket number).