OpenEdX does not currently offer built-in password protection, to lock an assessment from students accessing it until a password is entered. This makes it difficult to restrict access to students from submitting the assessment from off-campus (home). This workaround method is proposed to add password protection to an assessment.
Grading - Assignment Type
For each assessment that you wish to lock with a password, create a separate Assignment Type.
From the CMS, go to Settings → Grading.