How to make a signed request URL for Google Maps for Work API

gistfile1.m

#import <CommonCrypto/CommonDigest.h>
#import <CommonCrypto/CommonHMAC.h>

+ (NSString *)signedUrlFromUrl:(NSString *)fullURL {
    fullURL = [fullURL stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSString *unmodifiedKey = [@"Your Google Maps for Work API Key" stringByReplacingOccurrencesOfString:@"-" withString:@"+"];
    unmodifiedKey = [unmodifiedKey stringByReplacingOccurrencesOfString:@"_" withString:@"/"];
    
    NSData *keyData = [[NSData alloc] initWithBase64EncodedData:[unmodifiedKey dataUsingEncoding:NSUTF8StringEncoding] options:0];
    NSData *urlData = [fullURL dataUsingEncoding:NSUTF8StringEncoding];
    unsigned char hmac[CC_SHA1_DIGEST_LENGTH];
    
    CCHmac(kCCHmacAlgSHA1, [keyData bytes], keyData.length, [urlData bytes], urlData.length, &hmac);
    
    NSData *hashedData = [NSData dataWithBytes:hmac length:CC_SHA1_DIGEST_LENGTH];
    NSString *base64String = [hashedData base64EncodedStringWithOptions:0];
    base64String = [base64String stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    
    NSString *modifiedBase64String = [base64String stringByReplacingOccurrencesOfString:@"+" withString:@"-"];
    modifiedBase64String = [modifiedBase64String stringByReplacingOccurrencesOfString:@"/" withString:@"_"];
    
    NSString *signedURL = [fullURL stringByAppendingFormat:@"&signature=%@", modifiedBase64String];
    return signedURL;
}