The OAuth2 Authorization Framework (see RFC 6749) provides a web based mechanism to request claims based Access Tokens from an Authorization Service (AS) that is supported by many major companies providing cloud infrastructure. These Access Tokens are passed to by a Client to a Server in a UserIdentityToken as described in OPC 10000-4.
The OpenID Connect specification (see OpenID) builds on the OAuth2 specification by defining the contents of the Access Tokens more strictly.
The OAuth2 specification supports a number of use cases (called ‘flows’) to handle different application requirements. The use cases that are relevant to OPC UA are discussed below.