azure-functions-host: Azure Functions does not work if length of the request URL (with query-params) is > 2102

I use proxies for a SPA, and to handle OAuth2 authorization code grant flow. When my function app receives a redirect with the code, state, and id_token query params, I was noticing that the function wouldn’t even execute. There is no error in the logs either. So I tested by truncating the value of the query params and it turns out that if the length exceeds 2102, then the routing doesn’t work for some reason.

Investigative information

Note: I have provided information of a normal execution of my function. When the problem occurs, there is actually nothing in the logs that would indicate this problem. Furthermore, Proxy-Trace-Enabled header attribute doesn’t help either because no function has executed.

• Timestamp: 2018-01-19T05:42:29.349
• Function App version (1.0 or 2.0-beta): 1.0
• Function App name:
• Function name(s) (as appropriate): after-auth
• Invocation ID: a3df31ab-6fff-4517-b836-7170e245d1bd
• Region: West US

Repro steps

1. Create a proxy rule that invokes a function.
2. Call the function app so that the proxy rule is executed but with query-params with length > 2102.

Expected behavior

After step 2, the proxy rule would be invoked and the function should execute.

Actual behavior

• Browser receives a 404 Not Found HTTP status code.
• Proxy rule won’t be executed but instead you will get a response The resource you are looking for has been removed, had its name changed, or is temporarily unavailable.

Known workarounds

Use the request body instead of query-params.

Related information

• JS function
• HttpBinding

EDIT: I wanted to clarify that the length I am talking about is the total length of the URL with the query params, and not just the length of the query params put together. EDIT2: Updated the notes under Actual Behavior.