NSMutableURLRequest+Ghost.m

#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonHMAC.h>
#import <CoreFoundation/CoreFoundation.h>

static NSString *Base64URLEncodedStringWithData(NSData *data) {
    NSMutableString *string = [[data base64EncodedStringWithOptions:0] mutableCopy];
    [string replaceOccurrencesOfString:@"+" withString:@"-" options:0 range:NSMakeRange(0, string.length)];
    [string replaceOccurrencesOfString:@"/" withString:@"_" options:0 range:NSMakeRange(0, string.length)];
    [string replaceOccurrencesOfString:@"=" withString:@"" options:0 range:NSMakeRange(0, string.length)];
    return string.copy;
}

static NSData *DataWithHexString(NSString *hex) {
    if (hex.length % 2 == 0) {
        char buf[3];
        buf[2] = '\0';
        unsigned char *bytes = calloc(hex.length / 2, sizeof(unsigned char));
        unsigned char *bp = bytes;
        CFStringInlineBuffer inlineBuffer;
        CFStringInitInlineBuffer((__bridge CFStringRef)hex, &inlineBuffer, CFRangeMake(0, hex.length));
        for (CFIndex i = 0; i < hex.length; i += 2) {
            buf[0] = CFStringGetCharacterFromInlineBuffer(&inlineBuffer, i);
            buf[1] = CFStringGetCharacterFromInlineBuffer(&inlineBuffer, i + 1);
            char *b2 = NULL;
            *bp++ = strtol(buf, &b2, 16);
        }
        return [NSData dataWithBytesNoCopy:bytes length:hex.length / 2 freeWhenDone:YES];
    }
    return nil;
}

@implementation NSMutableURLRequest (Ghost)

+ (NSMutableURLRequest *)requestWithGhostAPIKey:(NSString *)APIKey APIURL:(NSURL *)APIURL endpoint:(NSString *)endpoint {
    NSArray<NSString *> *APIKeyComponents = [APIKey componentsSeparatedByString:@":"];
    NSString *kid = APIKeyComponents.count != 2 ? @"unknown" : APIKeyComponents[0];
    NSString *secret = APIKeyComponents.count != 2 ? @"unknown" : APIKeyComponents[1];
    
    NSDate *date = [NSDate date];
    NSDateComponents *expirationDateComponents = [[NSDateComponents alloc] init];
    expirationDateComponents.minute = 5;
    NSDate *expirationDate = [[NSCalendar currentCalendar] dateByAddingComponents:expirationDateComponents toDate:date options:0];
    
    NSError *JSONError;
    NSData *headerData = [NSJSONSerialization dataWithJSONObject:@{@"alg": @"HS256", @"kid": kid, @"typ": @"JWT"} options:0 error:&JSONError];
    NSData *payloadData = [NSJSONSerialization dataWithJSONObject:@{@"exp": @(lround(expirationDate.timeIntervalSince1970)), @"iat": @(lround(date.timeIntervalSince1970)), @"aud": @"/v2/admin/"} options:0 error:&JSONError];
    
    NSMutableArray<NSString *> *tokenComponents = [[NSMutableArray alloc] init];
    [tokenComponents addObject:Base64URLEncodedStringWithData(headerData)];
    [tokenComponents addObject:Base64URLEncodedStringWithData(payloadData)];
    
    NSData *data = [[tokenComponents componentsJoinedByString:@"."] dataUsingEncoding:NSUTF8StringEncoding];
    NSData *secretData = DataWithHexString(secret);
    NSMutableData *hmacData = [[NSMutableData alloc] initWithLength:CC_SHA256_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA256, secretData.bytes, secretData.length, data.bytes, data.length, hmacData.mutableBytes);
    [tokenComponents addObject:Base64URLEncodedStringWithData(hmacData)];
    
    NSString *token = [tokenComponents componentsJoinedByString:@"."];
    
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    request.URL = [NSURL URLWithString:[NSString pathWithComponents:@[@"/ghost/api/v2/admin/", endpoint]] relativeToURL:APIURL];
    [request setValue:[NSString stringWithFormat:@"Ghost %@", token] forHTTPHeaderField:@"Authorization"];
    return request;
}

@end