Adds or updates the policy that is specified as the IAM user's permissions boundary. You can use an Amazon Web Services managed policy or a customer managed policy to set the boundary for a user. Use the boundary to control the maximum permissions that the user can have. Setting a permissions boundary is an advanced feature that can affect the permissions for the user.

Policies that are used as permissions boundaries do not provide permissions. You must also attach a permissions policy to the user. To learn how the effective permissions for a user are evaluated, see IAM JSON policy evaluation logic in the IAM User Guide.