Set HTTP headers in Go by using the Header.Set method on Request or ResponseWriter objects, or control HTTP behavior via GODEBUG environment variables.
Set HTTP headers by assigning key-value pairs to the Header map on your http.Request or http.ResponseWriter object.
req.Header.Set("Content-Type", "application/json")
resp.Header.Set("X-Custom-Header", "value")
For environment-level HTTP behavior control, use the GODEBUG variable with settings like http2client=0 to disable HTTP/2.
HTTP headers are small pieces of information sent with web requests and responses to tell the server or browser how to handle the data. You set them to specify things like file types or custom rules. Think of them like the address label on an envelope that tells the post office where to send it and how to handle it.