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Via OIDC, clients can confirm the identity of an end user using authentication by an authorization server.
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Should only be used in case of a hybrid CMIS Scenario:
OauthToken AND open Documents from SAP in an external browser.
The tokenseckey authentication type is a combination of token authentication and SAP seckey. For SAP users, that need the Document opened in an external application (like a Browser), SAP created this process.
The procedure ensure, that the machine Token (configured in SAP) is not exposed to a Browser where it could easily extract and access other resources on the CMIS Server for that repository.
See following Documentations (sub-pages):
OpenID configuration - tokenseckey (tC)