objective_c-sample-oauth.objective-c

NSMutableData *data = [NSMutableData dataWithLength:32];
int result attribute((unused)) = SecRandomCopyBytes(kSecRandomDefault, 32, data.mutableBytes);
NSString *verifier = [[[[data base64EncodedStringWithOptions:0]
stringByReplacingOccurrencesOfString:@"+" withString:@"-"]
stringByReplacingOccurrencesOfString:@"/" withString:@"_"]
stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"="]];

// You need to import CommonCrypto
u_int8_t buffer[CC_SHA256_DIGEST_LENGTH * sizeof(u_int8_t)];
memset(buffer, 0x0, CC_SHA256_DIGEST_LENGTH);
NSData *data = [verifier dataUsingEncoding:NSUTF8StringEncoding];
CC_SHA256([data bytes], (CC_LONG)[data length], buffer);
NSData *hash = [NSData dataWithBytes:buffer length:CC_SHA256_DIGEST_LENGTH];
NSString *challenge = [[[[hash base64EncodedStringWithOptions:0]
stringByReplacingOccurrencesOfString:@"+" withString:@"-"]
stringByReplacingOccurrencesOfString:@"/" withString:@"_"]
stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@"="]];