Fix 2FA Remember to actually be 30 days (#6929)

Currently we always regenerate the 2FA Remember token, and always send that back to the client.
This is not the correct way, and in turn causes the remember token to never expire.

While this might be convenient, it is not really safe.
This commit changes the 2FA Remember Tokens from random string to a JWT.
This JWT has a lifetime of 30 days and is validated per device & user combination.

This does mean that once this commit is merged, and users are using this version, all their remember tokens will be invalidated.
From my point of view this isn't a bad thing, since those tokens should have expired already.

Only users who recently checked the remember checkbox within 30 days have to login again, but that is a minor inconvenience I think.

Signed-off-by: BlackDex <black.dex@gmail.com>

src/auth.rs

@@ -46,6 +46,7 @@ static JWT_FILE_DOWNLOAD_ISSUER: LazyLock<String> =
     LazyLock::new(|| format!("{}|file_download", CONFIG.domain_origin()));
 static JWT_REGISTER_VERIFY_ISSUER: LazyLock<String> =
     LazyLock::new(|| format!("{}|register_verify", CONFIG.domain_origin()));
+static JWT_2FA_REMEMBER_ISSUER: LazyLock<String> = LazyLock::new(|| format!("{}|2faremember", CONFIG.domain_origin()));
 
 static PRIVATE_RSA_KEY: OnceLock<EncodingKey> = OnceLock::new();
 static PUBLIC_RSA_KEY: OnceLock<DecodingKey> = OnceLock::new();
@@ -160,6 +161,10 @@ pub fn decode_register_verify(token: &str) -> Result<RegisterVerifyClaims, Error
     decode_jwt(token, JWT_REGISTER_VERIFY_ISSUER.to_string())
 }
 
+pub fn decode_2fa_remember(token: &str) -> Result<TwoFactorRememberClaims, Error> {
+    decode_jwt(token, JWT_2FA_REMEMBER_ISSUER.to_string())
+}
+
 #[derive(Debug, Serialize, Deserialize)]
 pub struct LoginJwtClaims {
     // Not before
@@ -440,6 +445,31 @@ pub fn generate_register_verify_claims(email: String, name: Option<String>, veri
     }
 }
 
+#[derive(Serialize, Deserialize)]
+pub struct TwoFactorRememberClaims {
+    // Not before
+    pub nbf: i64,
+    // Expiration time
+    pub exp: i64,
+    // Issuer
+    pub iss: String,
+    // Subject
+    pub sub: DeviceId,
+    // UserId
+    pub user_uuid: UserId,
+}
+
+pub fn generate_2fa_remember_claims(device_uuid: DeviceId, user_uuid: UserId) -> TwoFactorRememberClaims {
+    let time_now = Utc::now();
+    TwoFactorRememberClaims {
+        nbf: time_now.timestamp(),
+        exp: (time_now + TimeDelta::try_days(30).unwrap()).timestamp(),
+        iss: JWT_2FA_REMEMBER_ISSUER.to_string(),
+        sub: device_uuid,
+        user_uuid,
+    }
+}
+
 #[derive(Debug, Serialize, Deserialize)]
 pub struct BasicJwtClaims {
     // Not before