diff --git a/lib/uri_parser.js b/lib/uri_parser.js
index 8ff66b142..957d71ef2 100644
--- a/lib/uri_parser.js
+++ b/lib/uri_parser.js
@@ -451,6 +451,13 @@ function parseConnectionString(uri, options, callback) {
 
   parsedOptions = Object.assign({}, parsedOptions, options);
   const auth = { username: null, password: null, db: db && db !== '' ? qs.unescape(db) : null };
+  if (parsedOptions.auth) {
+    // maintain support for legacy options passed into `MongoClient`
+    if (parsedOptions.auth.username) auth.username = parsedOptions.auth.username;
+    if (parsedOptions.auth.user) auth.username = parsedOptions.auth.user;
+    if (parsedOptions.auth.password) auth.password = parsedOptions.auth.password;
+  }
+
   if (cap[4].split('?')[0].indexOf('@') !== -1) {
     return callback(new MongoParseError('Unescaped slash in userinfo section'));
   }
diff --git a/test/tests/unit/connection_string_tests.js b/test/tests/unit/connection_string_tests.js
index 30cfb75be..6234340bd 100644
--- a/test/tests/unit/connection_string_tests.js
+++ b/test/tests/unit/connection_string_tests.js
@@ -29,6 +29,38 @@ const skipTests = [
 ];
 
 describe('Connection String', function() {
+  it('should support auth passed in through options', function(done) {
+    const optionsWithUser = {
+      authMechanism: 'SCRAM-SHA-1',
+      auth: { user: 'testing', password: 'llamas' }
+    };
+
+    const optionsWithUsername = {
+      authMechanism: 'SCRAM-SHA-1',
+      auth: { username: 'testing', password: 'llamas' }
+    };
+
+    parseConnectionString('mongodb://localhost', optionsWithUser, (err, result) => {
+      expect(err).to.not.exist;
+      expect(result.auth).to.containSubset({
+        db: 'admin',
+        username: 'testing',
+        password: 'llamas'
+      });
+
+      parseConnectionString('mongodb://localhost', optionsWithUsername, (err, result) => {
+        expect(err).to.not.exist;
+        expect(result.auth).to.containSubset({
+          db: 'admin',
+          username: 'testing',
+          password: 'llamas'
+        });
+
+        done();
+      });
+    });
+  });
+
   it('should provide a default port if one is not provided', function(done) {
     parseConnectionString('mongodb://hostname', function(err, result) {
       expect(err).to.not.exist;