diff --git a/changelog.d/7147.doc b/changelog.d/7147.doc
new file mode 100644
index 0000000000..2c855ff5f7
--- /dev/null
+++ b/changelog.d/7147.doc
@@ -0,0 +1 @@
+Add documentation for running a local CAS server for testing.
diff --git a/docs/dev/cas.md b/docs/dev/cas.md
new file mode 100644
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+++ b/docs/dev/cas.md
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+# How to test CAS as a developer without a server
+
+The [django-mama-cas](https://github.com/jbittel/django-mama-cas) project is an
+easy to run CAS implementation built on top of Django.
+
+## Prerequisites
+
+1. Create a new virtualenv: `python3 -m venv <your virtualenv>`
+2. Activate your virtualenv: `source /path/to/your/virtualenv/bin/activate`
+3. Install Django and django-mama-cas:
+   ```
+   python -m pip install "django<3" "django-mama-cas==2.4.0"
+   ```
+4. Create a Django project in the current directory:
+   ```
+   django-admin startproject cas_test .
+   ```
+5. Follow the [install directions](https://django-mama-cas.readthedocs.io/en/latest/installation.html#configuring) for django-mama-cas
+6. Setup the SQLite database: `python manage.py migrate`
+7. Create a user:
+   ```
+   python manage.py createsuperuser
+   ```
+   1. Use whatever you want as the username and password.
+   2. Leave the other fields blank.
+8. Use the built-in Django test server to serve the CAS endpoints on port 8000:
+   ```
+   python manage.py runserver
+   ```
+
+You should now have a Django project configured to serve CAS authentication with
+a single user created.
+
+## Configure Synapse (and Riot) to use CAS
+
+1. Modify your `homeserver.yaml` to enable CAS and point it to your locally
+   running Django test server:
+   ```yaml
+   cas_config:
+     enabled: true
+     server_url: "http://localhost:8000"
+     service_url: "http://localhost:8081"
+     #displayname_attribute: name
+     #required_attributes:
+     #    name: value
+   ```
+2. Restart Synapse.
+
+Note that the above configuration assumes the homeserver is running on port 8081
+and that the CAS server is on port 8000, both on localhost.
+
+## Testing the configuration
+
+Then in Riot:
+
+1. Visit the login page with a Riot pointing at your homeserver.
+2. Click the Single Sign-On button.
+3. Login using the credentials created with `createsuperuser`.
+4. You should be logged in.
+
+If you want to repeat this process you'll need to manually logout first:
+
+1. http://localhost:8000/admin/
+2. Click "logout" in the top right.
diff --git a/docs/dev/saml.md b/docs/dev/saml.md
index f41aadce47..a9bfd2dc05 100644
--- a/docs/dev/saml.md
+++ b/docs/dev/saml.md
@@ -18,9 +18,13 @@ To make Synapse (and therefore Riot) use it:
        metadata:
          local: ["samling.xml"]   
    ```
-5. Run `apt-get install xmlsec1` and `pip install --upgrade --force 'pysaml2>=4.5.0'` to ensure
+5. Ensure that your `homeserver.yaml` has a setting for `public_baseurl`:
+   ```yaml
+   public_baseurl: http://localhost:8080/
+   ```
+6. Run `apt-get install xmlsec1` and `pip install --upgrade --force 'pysaml2>=4.5.0'` to ensure
    the dependencies are installed and ready to go.
-6. Restart Synapse.
+7. Restart Synapse.
 
 Then in Riot: