feat: add saml docs

src/data/docs/20-authentication/50-saml.md

@@ -0,0 +1,35 @@
+---
+title: 'SAML Authentication'
+sidebarTitle: 'SAML'
+excerpt: 'Authenticating to Meli using SAML'
+---
+
+# SAML Authentication
+
+**Warning:** Make sure to setup your private/public keys, or else SAML login will be insecure.
+
+1. Create a new SAML client in your IdP (for example, Keycloak) and remember the issuer/client name.
+1. Look at your IdP docs to find the corresponding endpoint (for keycloak it is `https://<my.keycloak.install>/auth/realms/<my.realm>/protocol/saml`)
+1. Look at your IdP docs to find your SAML certificate (for keycloak you can get it at `https://<my.keycloak.install>/auth/realms/<my.realm>/protocol/saml/descriptor`)
+1. Generate an RSA private/public keypair to use for signing requests, and configure your IdP with the public key.
+
+For information on how to format the certificate and key, see [the upstream passport-saml documentation](https://github.com/node-saml/passport-saml#security-and-signatures).
+
+Now, you can update your `docker-compose.yml`:
+
+<div class="code-group">
+
+```yaml
+services:
+  # ...
+  server:
+    # ...
+    environment:
+      # ...
+      MELI_SAML_ENDPOINT: <the-full-url-to-your-saml-endpoint>
+      MELI_SAML_ISSUER: <the-issuer-or-client-to-authenticate-as>
+      MELI_SAML_IDP_CRT: <the-public-cert-of-your-IdP>
+      MELI_SAML_PRIVATE_CRT: <an-RSA-private-key>
+``` 
+
+</div>