1. Navigate to My Users.
2. Select the user to enable.
3. Click Edit.
4. Click the Single Sign-On Enabled checkbox.
5. Enter the shared identifier in Federation ID. This value uniquely identifies the user for Single Sign-On authentication. This unique value is the value passed in the tag in the SAML assertions sent to Marketing Cloud, which identifies the user for Single Sign-On authentication. For example, if you use email address as your user identifier​,​ the Federation ID uses that user​'​s email address.
6. Click Save.