Enabled basic API Gateway support: enrolled "execute-api" in awsSignVersion and serviceAndRegion(host) parsing.

Author: brianfaull

awsauth.go

@@ -201,6 +201,7 @@ var (
 		"elasticmapreduce":     4,
 		"elastictranscoder":    4,
 		"elasticache":          2,
+		"execute-api":          4,
 		"glacier":              4,
 		"kinesis":              4,
 		"redshift":             4,

common.go

@@ -46,8 +46,14 @@ func serviceAndRegion(host string) (service string, region string) {
 			region = parts[1]
 		}
 	} else if len(parts) == 5 {
-		service = parts[2]
-		region = parts[1]
+		if parts[1] == "execute-api" { //TODO: is this the only service?
+			// API Gateway ("execute-api") has form 1234abcd56.execute-api.us-east-1.amazonaws.com
+			service = parts[1]
+			region = parts[2]
+		} else {
+			service = parts[2]
+			region = parts[1]
+		}
 	} else {
 		// Either service.amazonaws.com or s3-region.amazonaws.com
 		if strings.HasPrefix(parts[0], "s3-") {