Simple extension to AWSAPIGatewayClient rewritten for Swift 3 to automatically get configuration, and have a shared lazy instantiated client. Other code will call invokeHTTPRequest directly.

AWSAPIGatewayClientExtension.swift

/*
 Copyright 2010-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.

 Licensed under the Apache License, Version 2.0 (the "License").
 You may not use this file except in compliance with the License.
 A copy of the License is located at

 http://aws.amazon.com/apache2.0

 or in the "license" file accompanying this file. This file is distributed
 on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 express or implied. See the License for the specific language governing
 permissions and limitations under the License.
 */
 

import AWSCore
import AWSAPIGateway

extension AWSAPIGatewayClient
{

	static let AWSInfoClientKey = "ApiClientKey"
	static let AWSPath = "https://apipath"

	/**
	 Returns the singleton service client. If the singleton object does not exist, the SDK instantiates the default service client with `defaultServiceConfiguration` from `AWSServiceManager.defaultServiceManager()`. The reference to this object is maintained by the SDK, and you do not need to retain it manually.
	
	 If you want to enable AWS Signature, set the default service configuration in `func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?)`
	
	     func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
	         let credentialProvider = AWSCognitoCredentialsProvider(regionType: .USEast1, identityPoolId: "YourIdentityPoolId")
	         let configuration = AWSServiceConfiguration(region: .USEast1, credentialsProvider: credentialProvider)
	         AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = configuration
	
	         return true
	     }
	
	 Then call the following to get the default service client:
	
	     let serviceClient = AWSAPIGatewayClient.default()

     Alternatively, this configuration could also be set in the `info.plist` file of your app under `AWS` dictionary with a configuration dictionary by name `AWSAPIGatewayClient`.
	
	 @return The default service client.
	 */ 
	 
	static let _defaultClient:AWSAPIGatewayClient = 
	{
		var serviceConfiguration: AWSServiceConfiguration? = nil
		let serviceInfo = AWSInfo.default().defaultServiceInfo(AWSInfoClientKey)
		if let serviceInfo = serviceInfo {
			serviceConfiguration = AWSServiceConfiguration(region: serviceInfo.region, credentialsProvider: serviceInfo.cognitoCredentialsProvider)
		} else if (AWSServiceManager.default().defaultServiceConfiguration != nil) {
			serviceConfiguration = AWSServiceManager.default().defaultServiceConfiguration
		} else {
			serviceConfiguration = AWSServiceConfiguration(region: .unknown, credentialsProvider: nil)
		}
		
		return AWSAPIGatewayClient(configuration: serviceConfiguration!)
	}()

	public class func `default`() -> AWSAPIGatewayClient { return _defaultClient }

	convenience init(configuration: AWSServiceConfiguration) {
	    self.init()
	
		  self.configuration = configuration.copy() as! AWSServiceConfiguration
	    var URLString: String = AWSAPIGatewayClient.AWSPath
	    if URLString.hasSuffix("/") 
	    {
	    	URLString.remove(at: URLString.index(before: URLString.endIndex))
	    }
	    self.configuration.endpoint = AWSEndpoint(region: configuration.regionType, service: .apiGateway, url: URL( string:URLString )!)
	    let signer: AWSSignatureV4Signer = AWSSignatureV4Signer(credentialsProvider: configuration.credentialsProvider, endpoint: self.configuration.endpoint)
	    if let endpoint = self.configuration.endpoint 
	    {
	    	self.configuration.baseURL = endpoint.url
	    }
	    self.configuration.requestInterceptors = [AWSNetworkingRequestInterceptor(), signer]
	}

}