Azure AD error - 'IDX10311: RequireNonce is true but validationContext.Nonce is null'

I’ve experienced this one enough times now that I’d like to preserve the solution/s for future occurrences. The exact message is:

IDX10311: RequireNonce is ‘true’ (default) but validationContext.Nonce is null. A nonce cannot be validated. If you don’t need to check the nonce, set OpenIdConnectProtocolValidator.RequireNonce to ‘false’.
An easy way to reproduce this one is to hit the “back” button after having signed in to an ASP.NET web app that auths with Azure AD using the OWIN library.