fix: Add test and logic to ignore credentials if authSource is the only auth option

Author: nbbeeken

src/connection_string.ts

@@ -394,6 +394,16 @@ export function parseOptions(
     }
 
     mongoOptions.credentials.validate();
+
+    // Check if the only auth related option provided was authSource, if so we can remove credentials
+    if (
+      mongoOptions.credentials.password === '' &&
+      mongoOptions.credentials.username === '' &&
+      mongoOptions.credentials.mechanism === AuthMechanism.MONGODB_DEFAULT &&
+      Object.keys(mongoOptions.credentials.mechanismProperties).length === 0
+    ) {
+      delete mongoOptions.credentials;
+    }
   }
 
   if (!mongoOptions.dbName) {

test/unit/connection_string.test.ts

@@ -6,8 +6,13 @@ import { promisify } from 'util';
 import { MongoCredentials } from '../../src/cmap/auth/mongo_credentials';
 import { AUTH_MECHS_AUTH_SRC_EXTERNAL, AuthMechanism } from '../../src/cmap/auth/providers';
 import { parseOptions, resolveSRVRecord } from '../../src/connection_string';
-import { MongoDriverError, MongoInvalidArgumentError, MongoParseError } from '../../src/error';
-import { MongoOptions } from '../../src/mongo_client';
+import {
+  MongoDriverError,
+  MongoInvalidArgumentError,
+  MongoParseError,
+  MongoServerSelectionError
+} from '../../src/error';
+import { MongoClient, MongoOptions } from '../../src/mongo_client';
 
 describe('Connection String', function () {
   it('should not support auth passed with user', function () {
@@ -98,6 +103,24 @@ describe('Connection String', function () {
     expect(options).to.have.nested.property('credentials.source', mockAuthSource);
   });
 
+  it('should omit credentials if the only auth related option is authSource', async () => {
+    const client = new MongoClient('mongodb://localhost:123/?authSource=someDb', {
+      serverSelectionTimeoutMS: 500
+    });
+
+    let thrownError: Error;
+    try {
+      // relies on us not running a mongod on port 123, fairly likely assumption
+      await client.connect();
+    } catch (error) {
+      thrownError = error;
+    }
+
+    // We should fail to connect, not fail to find an auth provider
+    expect(thrownError).to.be.instanceOf(MongoServerSelectionError);
+    expect(client.options).to.not.have.a.property('credentials');
+  });
+
   it('should parse a numeric authSource with variable width', function () {
     const options = parseOptions('mongodb://test@localhost/?authSource=0001');
     expect(options.credentials.source).to.equal('0001');