Greetings!
The Last-Modified response header returns a non-standard formatted date at the moment.
Consider the following Last-Modified value, taken from the Game Data APIs:
Sun, 1 Mar 2020 15:06:18 GMT
The closest standard format is RFC1123, but this format requires the date field to be padded with a 0 for single digit days. A valid RFC1123 formatted date would be:
Sun, 01 Mar 2020 15:06:18 GMT
For clarity, see the following example on the Go Playground: https://play.golang.org/p/kCTFOSngr77
It is not a major problem since it is easy to create a workaround, but you might be under the impression that the Last-Modified header adheres to the RFC1123 format. Especially since double digit days do parse.