A User Grant is a way to directly assign a user to a Security Level, even if they do not meet the requirements of the Security Level Rules. User Grants essentially act as an override to the original rules of the Security Level.
User Grants are accessed from the Gateway Webpage Config section in Security > Identity Providers. Users can be added and edited using the buttons in the Users table so that Security Levels can then be granted to them.
Users are identified by either their username or their ID from the provider response document. Once you have identified a user, you can assign them any number of grants to Security Levels. Selecting a level will automatically select all security levels above it. The User Grants can only be applied to a user after they authenticate with the Identity Provider, though the grants do not have to be for levels within the Authenticated branch.