refactored HTTP header handling

request.go

@@ -121,7 +121,7 @@ func Method(method string) RequestModifier {
 	}
 }
 
-func Headers(keyValuePairs ...string) RequestModifier {
+func AddHeaders(keyValuePairs ...string) RequestModifier {
 	if len(keyValuePairs)%2 != 0 {
 		panic("keyValuePairs must have an even length")
 	}
@@ -143,7 +143,21 @@ func RemoveHeaders(headers ...string) RequestModifier {
 	}
 }
 
-func HeadersMap(headers map[string]string) RequestModifier {
+func RemoveAllHeaders() RequestModifier {
+	return func(r *RequestBuilder) *RequestBuilder {
+		r.Header = make(http.Header)
+		return r
+	}
+}
+
+func Headers(keyValuePairs ...string) RequestModifier {
+	return chainMods(
+		RemoveAllHeaders(),
+		AddHeaders(keyValuePairs...),
+	)
+}
+
+func AddHeadersMap(headers map[string]string) RequestModifier {
 	return func(r *RequestBuilder) *RequestBuilder {
 		for key, value := range headers {
 			r.Header.Add(key, value)
@@ -152,10 +166,17 @@ func HeadersMap(headers map[string]string) RequestModifier {
 	}
 }
 
+func HeadersMap(headers map[string]string) RequestModifier {
+	return chainMods(
+		RemoveAllHeaders(),
+		AddHeadersMap(headers),
+	)
+}
+
 func Auth(auth AuthProvider) RequestModifier {
 	return chainMods(
 		RemoveHeaders("Authorization"),
-		Headers("Authorization", auth()),
+		AddHeaders("Authorization", auth()),
 	)
 }