fix(claims): deser exact integer timestamp values from claims

[ocn]

When deserializing JWT claims from JSON inputs, the hardcoded values for issued_at, expires_at, invalid_before, etc. are bit-shifted to values which do not match the input. This PR uses UnixTimestamp methods which passthrough the values from the deserializer's input so that the resultant claims match the expected values from the input.

[ocn]

e.g. when deserializing the following input claims, the resultant issued_at time becomes 858993459200 due to the internal bit-shifting, rather than the desired test data.

    pub const TEST_CLAIMS: &str = r#"
    {
        "name": "Ada Lovelace",
        "iss": "https://chronogears.com/test",
        "aud": "test",
        "auth_time": 100,
        "user_id": "uid123",
        "sub": "sbu123",
        "iat": 200,
        "exp": 500,
        "nbf": 300,
        "email": "alovelace@chronogears.com"
    }"#;

    #[derive(Serialize, Deserialize, Debug)]
    pub struct CustomClaims {
        auth_time: i64,
        name: String,
        user_id: String,
        email: String,
    }

    #[test]
    fn my_cool_fn() {
        let claims: JWTClaims<CustomClaims> = serde_json::from_str(TEST_CLAIMS).unwrap();
        assert_eq!(claims.issued_at.unwrap(), 858993459200);
    }

With these changes, the claims are deserialized precisely to match the input data.

If there is some non-obvious reason why this should not be done and the input should in fact be bit-shifted, I would appreciate any insight you can share as to the reason why that is so.

[jedisct1]

    assert_eq!(claims.issued_at.unwrap(), 858993459200);

That should not even compile. issued.at is a Duration value, so if you want to get it as a number of seconds, use .as_secs():

    let claims: JWTClaims<NoCustomClaims> = serde_json::from_str(json).unwrap();
    assert_eq!(claims.issued_at.unwrap().as_secs(), 200);

[ocn]

That example will compile with an .into() call appended, which I accidentally omitted from my comment.

The issue is not that the deserialization does not directly store the input-values, but that JWTs created with the claims provided above cannot be verified due to "clock drift".

The following JWT and RS256 public-key pair cannot be verified, even though they are valid. I have provided a reproducible example below, with the imports omitted.

#[test_log::test]
fn should_verify() {
    #[derive(Serialize, Deserialize, Debug)]
    pub struct CustomClaims {
        auth_time: i64,
        name: String,
        user_id: String,
        email: String,
    }
    let key = RS256PublicKey::from_pem(r#"-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAt5N44H1mpb5Wlx/0e7Cd
oKTY8xt+3yMby8BgNdagVNkeCkZ4pRbmQXRWNC7qn//Zaxx9dnzHbzGCul5W0RLf
d3oB3PESwsrQh+oiXVEPTYhvUPQkX0vBfCXJtg/zY2mY1DxKOIiXnZ8PaK/7Sx0a
MmvR//0Yy2a5dIAWCmjPsxn+PcGZOkVUm+D5bH1+ZStcA/68r4ZSPix7Szhgl1Ro
Hb9Q6JSekyZqM0Qfwhgb7srZVXC/9/m5PEx9wMVNYpYJBrXhD5IQm9RzE9oJS8T+
Ai+4/5mNTNXI8f1rrYgffWS4wf9cvsEihrvEg9867B2f98L7ux9Llle7jsHCtwgV
1wIDAQAB
-----END PUBLIC KEY-----"#).unwrap();
    let jwt = "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6IjEifQ.eyJuYW1lIjoiQWRhIExvdmVsYWNlIiwiaXNzIjoiaHR0cHM6Ly9jaHJvbm9nZWFycy5jb20vdGVzdCIsImF1ZCI6InRlc3QiLCJhdXRoX3RpbWUiOjEwMCwidXNlcl9pZCI6InVpZDEyMyIsInN1YiI6InNidTEyMyIsImlhdCI6MjAwLCJleHAiOjUwMCwibmJmIjozMDAsImVtYWlsIjoiYWxvdmVsYWNlQGNocm9ub2dlYXJzLmNvbSJ9.eTQnwXrri_uY55fS4IygseBzzbosDM1hP153EZXzNlLH5s29kdlGt2mL_KIjYmQa8hmptt9RwKJHBtw6l4KFHvIcuif86Ix-iI2fCpqNnKyGZfgERV51NXk1THkgWj0GQB6X5cvOoFIdHa9XvgPl_rVmzXSUYDgkhd2t01FOjQeeT6OL2d9KdlQHJqAsvvKVc3wnaYYoSqv2z0IluvK93Tk1dUBU2yWXH34nX3GAVGvIoFoNRiiFfZwFlnz78G0b2fQV7B5g5F8XlNRdD1xmVZXU8X2-xh9LqRpnEakdhecciFHg0u6AyC4c00rlo_HBb69wlXajQ3R4y26Kpxn7HA";
    let verification = VerificationOptions {
        allowed_issuers: Some(HashSet::from(["https://chronogears.com/test".to_owned()])),
        artificial_time: Some(UnixTimeStamp::from_ticks(400)),
        time_tolerance: Some(coarsetime::Duration::from_secs(0)),
        ..Default::default()
    };
    key.verify_token::<CustomClaims>(jwt, Some(verification)).unwrap();
}

This results in an error/panic with the following message:

called `Result::unwrap()` on an `Err` value: Clock drift detected

When I use the changes I submitted in this PR, it does correctly deserialize the values as they are in the input data, which allows for the verification to proceed as expected.

[jedisct1]

You're trying to verify a token that was issued in year 1970.

UnixTimeStamp::from_ticks(400)

If 400 is a number of seconds, use from _secs().

ticks is just an internal, unstable, undocumented, non-portable representation.