Document OIDC authentication middleware usage with GitHub Actions

Signed-off-by: John Andersen <johnandersenpdx@gmail.com>

docs/oidc.md

@@ -0,0 +1,23 @@
+# OIDC Support
+
+- References
+  - [5.1.1.1.1.](https://github.com/ietf-wg-scitt/draft-ietf-scitt-architecture/blob/main/draft-ietf-scitt-architecture.md#comment-on-oidc)
+
+[![asciicast-of-oidc-auth-issued-by-github-actions](https://asciinema.org/a/607600.svg)](https://asciinema.org/a/607600)
+
+## Dependencies
+
+Install the SCITT API Emulator with the `oidc` extra.
+
+```console
+$ pip install -e .[oidc]
+```
+
+## Usage example with GitHub Actions
+
+See [`notarize.yml`](../.github/workflows/notarize.yml)
+
+References:
+
+- https://docs.github.com/en/actions/deployment/security-hardening-your-deployments/using-openid-connect-with-reusable-workflows
+- https://docs.github.com/en/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect