Every authentik install generates a self-signed certificate on the first start. The certificate is called _authentik Self-signed Certificate_ and is valid for 1 year.
This certificate is generated to be used as a default for all OAuth2/OIDC providers, as these don't require the certificate to be configured on both sides (the signature of a JWT is validated using the [JWKS](https://auth0.com/docs/security/tokens/json-web-tokens/json-web-key-sets) URL).
This certificate can also be used for SAML Providers/Sources, just keep in mind that the certificate is only valid for a year. Some SAML applications require the certificate to be valid, so they might need to be rotated regularly.
Starting with authentik 2021.12.4, you can configure the certificate authentik uses for its core webserver. For most deployments this will not be relevant and reverse proxies are used, but this can be used to create a very compact and self-contained authentik install.
To use let's encrypt certificates with this setup, using certbot, you can use this compose override (create or edit a file called `docker-compose.override.yml` in the same folder as the authentik docker-compose file)
Afterwards, run `docker-compose up -d`, which will start certbot and generate your certificate. Within a few minutes, you'll see the certificate in your authentik interface. (If the certificate does not appear, restart the worker container. This is caused by incompatible permissions set by certbot).