Ory is the largest open source community in the world for cloud software application security. We maintain advanced open source security software solving authentication, authorization, access control, application network security, and delegation. Ory implements a variety of industry and best-practice standards including OAuth 2.0 / OAuth 2.1, OpenID Connect, Zero Trust Networking, Google Zanzibar Policy Framework, FIDO2 U2F, WebAuthn, TOTP, and more.

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I noticed there are a lot more things documented that the gRPC API can do compared with what's documented from the REST API, and I was wondering if the REST API can do them but it's not documented? or if I should use the gRPC API for stuff like listing relation tuples?

REST supports approximately the same stuff as gRPC, see the reference at <https://www.ory.sh/docs/keto/reference/rest-api>