Impossible to override default headers

[williamlian]

zanzibar/runtime/client_http_request.go

Line 144 in 2939c4d

httpReq.Header.Add(headerKey, headerValue)

New headers are always "added" to the default one. This makes it impossible to override headers. For example, I have a default source header as "foo", but in my client code, I passed my header with source: bar. The result in this code will be source: foo, bar which will cause trouble if the remote endpoint checks for specific source. Can we have some mechanism to allow header override?

[ChuntaoLu]

Would not setting the default headers for the client solve the problem?