Rust

If you are looking to do something like Github's Personal Access Tokens (PAT) then it is easiest to just think about it like a password:

• Create a high entropy (secure) string
• Store the hash of the string in a database table
• Store the permissions and other metadata with the PAT's hash
• Validate the PAT (permissions, revoke status, etc) on each request to the server

Storing the hash of the token, like you do with passwords, is a good practice in case your db is ever compromised as it wont leave the tokens accessible and reusable without a lot of effort.

That depends on scale. For our IOT device, we just had a private key on the device and gave the customer an encrypted packet that had their privileges spelled out, and set a field on their user account appropriately. That wouldn't be secure at scale, but it worked really well for our B2B app.

If I were doing something at scale, I'd follow suggestions from others here.

I'd recommend switching away from Rocket if you can. It is not very actively maintained and Axum has become the better choice.

This is more of a cryptography question than a Rust question, but typically you'll use a so-called key diversification function (KDF) for this. See: https://en.wikipedia.org/wiki/Key_derivation_function (another term for the same thing, with slightly different connotations).

For an API key, you might have a user ID sent in the clear, and a secret key SK on the server. The KDF you would use would be something like HMAC-SHA256 truncated to 128 bits. Then the API key would be KDF(SK, ID). You will want a way to invalidate ID's and issue new ones so the person can cycle or change their API key. You could add a parameter P to the UID for this purpose, but again you have to be able to invalidate it.

You want to be very careful with SK on the server side. In financial apps (where the key can steal real money) you'd encapsulate it in a hardware security module (HSM). For less high-value apps you could still wrap it in its own HSM-like interface in its own process, that the rest of the app queries through a local socket. The idea is that the KDF process has a smaller attack surface than the big complicated web app. It can also implement throttling (limit the number of queries per second) in case a compromise app starts trying to spew API keys, and so on.

Added: your idea of just generating keys randomly and storing them in the database is also ok, but again you have to pay some attention to security, dealing with the possibility of the key table spilling, etc.