How to delete all keychain items accessible to an app?

Do it for all classes

Objective-C:

NSArray *secItemClasses = @[(__bridge id)kSecClassGenericPassword,
                       (__bridge id)kSecClassInternetPassword,
                       (__bridge id)kSecClassCertificate,
                       (__bridge id)kSecClassKey,
                       (__bridge id)kSecClassIdentity];
for (id secItemClass in secItemClasses) {
    NSDictionary *spec = @{(__bridge id)kSecClass: secItemClass};
    SecItemDelete((__bridge CFDictionaryRef)spec);
}

Swift:

let secItemClasses = [kSecClassGenericPassword, kSecClassInternetPassword, kSecClassCertificate, kSecClassKey, kSecClassIdentity]
for itemClass in secItemClasses {
    let spec: NSDictionary = [kSecClass: itemClass]
    SecItemDelete(spec)
}