How to test SAML as a developer without a server

https://fujifish.github.io/samling/samling.html (https://github.com/fujifish/samling) is a great resource for being able to tinker with the SAML options within Synapse without needing to deploy and configure a complicated software stack.

To make Synapse (and therefore Element) use it:

1. Use the samling.html URL above or deploy your own and visit the IdP Metadata tab.
2. Copy the XML to your clipboard.
3. On your Synapse server, create a new file samling.xml next to your homeserver.yaml with the XML from step 2 as the contents.
4. Edit your homeserver.yaml to include:

   saml2_config:
     sp_config:
       allow_unknown_attributes: true  # Works around a bug with AVA Hashes: https://github.com/IdentityPython/pysaml2/issues/388
       metadata:
         local: ["samling.xml"]
   

5. Ensure that your homeserver.yaml has a setting for public_baseurl:

   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.
7. Restart Synapse.

Then in Element:

1. Visit the login page and point Element towards your homeserver using the public_baseurl above.
2. Click the Single Sign-On button.
3. On the samling page, enter a Name Identifier and add a SAML Attribute for uid=your_localpart. The response must also be signed.
4. Click "Next".
5. Click "Post Response" (change nothing).
6. You should be logged in.

If you try and repeat this process, you may be automatically logged in using the information you gave previously. To fix this, open your developer console (F12 or Ctrl+Shift+I) while on the samling page and clear the site data. In Chrome, this will be a button on the Application tab.