ADFS : MSIS7042 - The same client browser session has made '6' requests

The full error message is:

Exception details: Microsoft.IdentityServer.Web.InvalidRequestException: MSIS7042: The same client browser session has made '6' requests in the last '7' seconds. Contact your administrator for details.

There are many causes for this; one being the "missing /" on the identifier.

I found one recently where I was running an ASP.NET MVC application inside VS that was authenticated via ADFS. This used the OWIN WS-Fed middleware.

I couldn't authenticate because of this error.

ADFS will only accept https connections so the RP was configured with a:

https://localhost/...

endpoint

But on VS, inside "Properties / Web", I noticed that the URL was:

 http://localhost/...

Setting this to https fixed the problem.

Go figure.

I found a similar solution here.

Enjoy!