> For the complete documentation index, see [llms.txt](https://standards.spdci.org/standards/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://standards.spdci.org/standards/dci-standards/id-systems-v1.0.0/wip-id-systems-and-sp-system-interface/1.-crvs/api.md).

# API

The APIs adopt the [**OpenID Connect** ](https://openid.net/specs/openid-connect-core-1_0.html)specification as the basis for authentication between SP-systems and ID-systems. Where required, [**custom claims**](mailto:undefined) can be defined to represent attributes such as identifiers and addresses, particularly in cases where these do not align in cardinality or data type with typical data objects.

In addition,  [**Verifiable Credentials (VC) API**](https://www.w3.org/TR/vc-api/) have been adopted as the standard mechanism for issuing credentials. This ensures secure, interoperable, and standards-based credential management across systems. Claim 169 is also suggested for QR code specification format for VCs.


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