  Self-Sovereign Identity (SSI), as a new and promising identity management
paradigm, needs mechanisms that can ease a gradual transition of existing
services and developers towards it. Systems that bridge the gap between SSI and
established identity and access management have been proposed but still lack
adoption. We argue that they are all some combination of too complex, locked
into specific ecosystems, have no source code available, or are not
sufficiently documented. We propose a comparatively simple system that enables
SSI-based sign-ins for services that support the widespread OpenID Connect or
OAuth 2.0 protocols. Its handling of claims is highly configurable through a
single policy and designed for cross-device authentication flows involving a
smartphone identity wallet. For external interfaces, we solely rely on open
standards, such as the recent OpenID for Verifiable Credentials standards. We
provide our implementation as open-source software intended for prototyping and
as a reference. Also, we contribute a detailed technical discussion of our
particular sign-in flow. To prove its feasibility, we have successfully tested
it with existing software and realistic hardware.
