Trying to get a simple download URL to work

TVDownloadLink

+(NSString *)createDownloadLinkForVaultID:(NSString *)vaultID blobID:(NSString *)blobID accessKey:(NSString *)accessKey secretKey:(NSString *)secretKey expiration:(NSDate *)expirationDate{
    NSString *expiration = @"2015-03-26T01:01:00+00:00";
    
    NSString *key = secretKey;
    NSString *data = expiration;
    const char *cKey = [key cStringUsingEncoding:NSUTF8StringEncoding];
    const char *cData = [data cStringUsingEncoding:NSUTF8StringEncoding];
    unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
    NSData *hash = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];
    NSString *signature = [hash base64EncodedStringWithOptions:0];
    
    NSDictionary *json = @{@"vault_id":vaultID,
                           @"blob_id":blobID};
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:json
                                                       options:0
                                                         error:nil];
    NSString *request = [jsonData base64EncodedStringWithOptions:0];
    
    
    NSMutableString *baseURL = [[NSMutableString alloc] initWithString:@"https://api.truevault.com/v1/download?"];
    [baseURL appendFormat:@"access_key=%@&", accessKey];
    [baseURL appendFormat:@"expiration=%@&", expiration];
    [baseURL appendFormat:@"signature=%@&", signature];
    [baseURL appendFormat:@"request=%@", request];
    return [NSString stringWithString:baseURL];
}