Prevent Duplicate `GrantedAuthority#getAuthority()` at time of Authentication

[rwinch]

If the GrantedAuthority is not equal, but contains a duplicate GrantedAuthority#getAuthority() then at the time of authentication, the Filter or WebFilter will duplicate the GrantedAuthority which leads to a memory leak. This is important to avoid for when we add support for a GrantedAuthority that might have an issuedAt attribute. If it is too old, then we'd want only the new GrantedAuthority to be added and the old instance to be removed. However, the two GrantedAuthority instances will not be equal because the issuedAt will not be equal.