(Objective-C) Generate an AWS (S3) Pre-Signed URL using Signature V4

Demonstrates how to generate a pre-signed URL using AWS Signature Version 4. This example generates a pre-signed URL for the Amazon S3 service.

Note: this example requires Chilkat v9.5.0.66 or greater.

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#import <CkoHttp.h>
#import <NSString.h>

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// Note: This example requires Chilkat v9.5.0.66 or greater.

CkoHttp *http = [[CkoHttp alloc] init];

http.AwsAccessKey = @"AWS_ACCESS_KEY";
http.AwsSecretKey = @"AWS_SECRET_KEY";

// Make sure to set your AWS region correctly
http.AwsRegion = @"us-east-1";

NSString *bucketName = @"chilkat100";
NSString *objectName = @"starfish/starfish.jpg";
NSString *localFilePath = @"qa_output/starfish.jpg";
NSString *awsService = @"s3";

// The signed URL will be valid for this number of seconds:
int numSecondsValid = 86400;

// Choose between a URL beginning with "http://" or "https://"...
BOOL bUseHttps = NO;

// Generate the pre-signed URL
NSString *preSignedUrl = [http S3_GenerateUrlV4: bUseHttps bucketName: bucketName path: objectName numSecondsValid: [NSNumber numberWithInt: numSecondsValid] awsService: awsService];
if (http.LastMethodSuccess != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

// The following URL can be copy-and-pasted into a browser..
NSLog(@"%@%@",@"Pre-Signed AWS S3 URL: ",preSignedUrl);

// Here's an example of a pre-signed URL. 
// This URL will only work within 1 day (86400 seconds) after the time this example was published.
// 
//     http://chilkat100.s3.amazonaws.com/starfish/starfish.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=16QXXDGY83AJJR6RVQ02%2F20170111%2Fus-west-2%2Fs3%2Faws4_request&X-Amz-Date=20170111T161959Z&X-Amz-Expires=86400&X-Amz-SignedHeaders=host&X-Amz-Signature=72bf4fd9a15d7bbcdd313a3318d937a778905f62a3fbff9b789d8dc28acd9232

// Now try to do an HTTP Download using the signed URL.
BOOL success = [http Download: preSignedUrl saveToPath: @"qa_output/starfish.jpg"];
if (success != YES) {
    NSLog(@"%@",http.LastErrorText);
}
else {
    NSLog(@"%@",@"Success.");
}