FR: Add option for hash input order when importing users

[jwngr]

Feature Request Description

Add a new hash.inputOrder option for the importUsers() auth method, inspired by the --hash-input-order parameter of the Firebase CLI.

It will accept a string value of "SALT_FIRST" or "PASSWORD_FIRST" and it will only apply to the SHA512, SHA256, SHA1, MD5, HMAC_SHA512, HMAC_SHA256, HMAC_SHA1, and HMAC_MD5 algorithms.

Usage Example

const importOptions = {
 hash: {
 algorithm: 'SHA256',
 rounds: 80,
 inputOrder: 'PASSWORD_FIRST', // or 'SALT_FIRST'
 }
};

return admin.auth().importUsers(users, importOptions)
 .then((results) => {
 console.log('Users successfully imported!', results);
 })
 .catch((error) => {
 console.log('Failed to import users:', error);
 });