Migrating user authentication from ForgeRock to another platform without knowing users' passwords involves transferring password hashes, salts, and the number of hashing iterations. Password hashing is a process where a string is transformed using an algorithm to produce a hash, which, when secure, is not reversible to its original form. Hashing functions like SHA-256, PBKDF2, and Bcrypt are commonly used, and the addition of a salt ensures unique hashes for identical passwords. Iterations refer to the repeated application of the hashing algorithm, enhancing security by slowing down potential attackers. ForgeRock uses PBKDF2-HMAC-SHA256 for hashing, storing the hash and salt in a base64 encoded format. By understanding and decoding this format, it is possible to obtain the necessary components to recreate the same hash in a new system, allowing seamless user migration without password resets.