  Identity and access management (I&AM) is the umbrella term for managing users
and their permissions. It is required for users to access different services.
These services can either be provided from their home organization, like a
company or university, or from external service providers, e.g., cooperation
partners. I&AM provides the management of identifiers with the attributes,
credentials, roles, and permissions the user has. Today, the requirements have
evolved from simply accessing individual web services in the internet or at a
company to the majority of all IT services from different service providers
with various accounts. Several identity management models have been created
with different approaches within.
  In order to adjust to heterogeneous environments, use cases, and the
evolution of identity management, this paper extends known requirements for
identity management. Existing models and approaches for identity management are
mapped to the derived requirements. Based on the mapping, advantages,
disadvantages, and gaps are identified. Current approaches suffer, as an
example, from trustworthiness and liability issues. Interoperability issues are
even more inherent as the approaches partly develop apart, forming an
heterogeneous environment. The results from this analysis emphasize the need
for one holistic identity management framework.
