All passwords stored with one-way hashes
Unique salts per user
Upgradable cryptography algorithms and hash strengths
Indicates when passwords should be rehashed to gradually upgrade password cryptography
Configurable hashing routines

Usage

Create a Crypto object, which will hold the cryptography routines used. Pass the algorithms you wish to use as arguments. The first algorithm will be used for storing passwords, the other algorithms are accepted for existing passwords (see Password Upgrades below).

passwords := pwcrypto.New(
    NewArgon2Crypto(),
    NewScryptCrypto(),
    NewPBKDF2Crypto(),
    NewSHA256Crypto(),
)

Use Hash() when storing a password for a user:

hash, err := passwords.Hash("mySecurePassword")

The value of hash is a string containing the hashed password and a set of configuration parameters used for verifying the password. Store this string in your database.

Use Check() for validating passwords:

valid, mustUpgrade, err := passwords.Check("someUserInput", hash)

In the above:

hash is the value you previously stored in your database, look it up for the user trying to authenticate
"someUserInput" is the password entered during login
valid indicates whether the input is correct
mustUpgrade indicates that the password needs to be upgraded (see below).

Password Upgrades

During check, mustUpgrade will be true if the database hash uses an outdated hash. In this case you should use Hash() again with the user input and store the new hashed value in your database.

This allows you to to upgrade your database gradually. Suppose you previously used SHA1, but want to upgrade to SHA256. Just configure pwcrypto with SHA256 as the primary algorithm and SHA1 as the fallback algorithm.

passwords := pwcrypto.New(
    NewSHA256Crypto(),
    NewSHA1Crypto(),
)

Whenever a user logs in correctly, you'll receive mustUpgrade == true. At this point you can use the user input to re-hash the password, which will then use SHA256.

Configuring hashing algorithms

By default, the unparametrized algorithm constructor will return a best-practices version of the algorithm.

You can use the more verbose constructor to override specific options (if any).

PBKDF2

Default: NewPBKDF2Crypto()
Verbose: NewPBKDF2CryptoWithOptions(iter, keyLen, saltLen int, hashFns []HashFunction)

Allows you to override the number of iterations, key length, salt length and hashing functions (for HMAC). Similar to crypto algorithms, the first hash function is preferred, others are for fallback compatibility.