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Troubleshooting

401 Unauthorized

  • Double-check that the request to the hub includes an authorization cookie (the default name is mercureAuthorization) or an Authorization HTTP header

  • If the cookie isn't set, you may have to explicitly include the request credentials (new EventSource(url, {withCredentials: true}) and fetch(url, {credentials: 'include'}))

  • Check the logs written by the hub on stderr, they contain the exact reason why the token has been rejected

  • Be sure to set a secret key (and not a JWT) in JWT_KEY (or in SUBSCRIBER_JWT_KEY and PUBLISHER_JWT_KEY)

  • If the secret key contains special characters, be sure to escape them properly, especially if you set the environment variable in a shell, or in a YAML file (Kubernetes...)

  • The publisher always needs a valid JWT, even if the anonymous directive is present in the Caddyfile, this JWT must have a property named publish. To dispatch private updates, the publish property must contain the list of topic selectors this publisher can use (example)

  • The subscriber needs a valid JWT only if the anonymous directive isn't present in the Caddyfile, or to subscribe to private updates, in this case the JWT must have a property named subscribe and containing an array of topic selectors (example)

For both the publish property, the array can be empty to publish only public updates. For both publish and subscribe, you can use ["*"] to match all topics.

CORS Issues

If the app connecting to the Mercure hub and the hub itself are not served from the same domain, you must whitelist the domain of the app using the CORS (Cross-Origin Resource Sharing) mechanism. The usual symptoms of a CORS misconfiguration are errors about missing CORS HTTP headers in the console of the browser (Refused to connect to 'https://hub.example.com/.well-known/mercure?topic=foo' because it violates the following Content Security Policy directive with Chrome, Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://hub.example.com/.well-known/mercure?topic=foo. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing) with Firefox).

To fix these errors, set the list of domains allowed to connect to the hub as value of the cors_origins in the Caddyfile. Example: cors_origins https://example.com https://example.net. Don't forget the https:// prefix before the domain name!

If you use an authorization mechanism (cookie or Authorization header), you cannot set the value of cors_origins to *. You must explicitly set the list of allowed origins. If you don't use an authorization mechanism (anonymous mode), you can set the value of cors_origins to * to allow all applications to connect to the hub (be sure to understand the security implications of what you are doing).

URI Templates and Topics

Try our URI template tester to ensure that the template matches the topic.

Mac OS Localhost Installation Error

How to process for Mercure to work in Mac OS Catalina:

  • In the Finder on your Mac, locate the app that you want to open

  • Control-click on the app icon, then choose "Open" from the shortcut menu

  • Click "Open"

Then you will have a warning, ignore it and close the Terminal.

Open a new Terminal in the Mercure folder.

Then just start the server:

./mercure run

It will work. 🎊