Crate macaroon

Implementation of Macaroons for Rust, which are flexible authorization tokens for distributed systems. They are similar to cookies, but allow for more narrowly-focused authorization based on contextual caveats.

What Are Macaroons?

Macaroons are bearer tokens (similar to cookies) which encode within them criteria within which the authorization is allowed to take place (referred to as “caveats”). For instance, authorization could be restricted to a particular user, account, time of day, really anything. These criteria can be either evaluated locally (a “first-party caveat”), or using special macaroons (“discharge macaroons”) generated by a third party (a “third-party caveat”).

A first-party caveat consists simply of a predicate which, when evaluated as true, authorizes the caveat. The predicate is a string which is either evaluated using strict string comparison (satisfy_exact), or interpreted using a provided function (satisfy_general).

A third-party caveat consists of a location string, an identifier, and a specially-generated signing key to authenticate the generated discharge macaroons. The key and identifier is passed to the third-party who generates the discharge macaroons. The receiver then binds each discharge macaroon to the original macaroon.

During verification of a third-party caveat, a discharge macaroon is found from those received whose identifier matches that of the caveat. The binding signature is verified, and the discharge macaroon’s caveats are verified using the same process as the original macaroon.

The macaroon is considered authorized only if all its caveats are authorized by the above process.

Example

use macaroon::{Macaroon, Verifier, MacaroonKey};

// Initialize to make crypto primitives thread-safe
macaroon::initialize().unwrap(); // Force panic if initialization fails

// Create our key
let key = MacaroonKey::generate(b"key");

// Create our macaroon. A location is optional.
let mut macaroon = match Macaroon::create(Some("location".into()), &key, "id".into()) {
    Ok(macaroon) => macaroon,
    Err(error) => panic!("Error creating macaroon: {:?}", error),
};

// Add our first-party caveat. We say that only someone with account 12345678
// is authorized to access whatever the macaroon is protecting
// Note that we can add however many of these we want, with different predicates
macaroon.add_first_party_caveat("account = 12345678".into());

// Now we verify the macaroon
// First we create the verifier
let mut verifier = Verifier::default();

// We assert that the account number is "12345678"
verifier.satisfy_exact("account = 12345678".into());

// Now we verify the macaroon. It should return `Ok(true)` if the user is authorized
match verifier.verify(&macaroon, &key, Default::default()) {
    Ok(_) => println!("Macaroon verified!"),
    Err(error) => println!("Error validating macaroon: {:?}", error),
}

// Now, let's add a third-party caveat, which just says that we need our third party
// to authorize this for us as well.

// Create a key for the third party caveat
let other_key = MacaroonKey::generate(b"different key");

macaroon.add_third_party_caveat("https://auth.mybank", &other_key, "caveat id".into());

// When we're ready to verify a third-party caveat, we use the location
// (in this case, "https://auth.mybank") to retrieve the discharge macaroons we use to verify.
// These would be created by the third party like so:
let mut discharge = match Macaroon::create(Some("http://auth.mybank/".into()),
                                           &other_key,
                                           "caveat id".into()) {
    Ok(discharge) => discharge,
    Err(error) => panic!("Error creating discharge macaroon: {:?}", error),
};
// And this is the criterion the third party requires for authorization
discharge.add_first_party_caveat("account = 12345678".into());

// Once we receive the discharge macaroon, we bind it to the original macaroon
macaroon.bind(&mut discharge);

// Then we can verify using the same verifier (which will verify both the existing
// first-party caveat and the third party one)
match verifier.verify(&macaroon, &key, vec![discharge]) {
    Ok(_) => println!("Macaroon verified!"),
    Err(error) => println!("Error validating macaroon: {:?}", error),
}

Supported Features

This crate supports all the following features:

• verification of first-party caveats either via exact string match or passed-in function
• verification of third-party caveats using discharge macaroons (including ones that themselves have embedded third-party caveats)
• serialization and deserialization of caveats via version 1, 2 or 2J serialization formats (fully compatible with libmacaroons)

Structs

ByteString

Macaroon

MacaroonKey

Secret cryptographic key used to sign and verify Macaroons.

Verifier

Enums

Caveat

Format

MacaroonError

Represents all of the errors that can arise when creating, deserializing, or verifying macaroons.

Functions

initialize

Initializes the cryptographic libraries. Although you can use macaroon without calling this, the underlying random-number generator is not guaranteed to be thread-safe if you don’t.

Type Definitions

Result

VerifyFunc