Some guidelines in designing the new validation API
* Previously, the `Valid` method was placed on the claim, which was always not entirely semantically correct, since the validity is concerning the token, not the claims. Although the validity of the token is based on the processing of the claims (such as `exp`). Therefore, the function `Valid` was removed from the `Claims` interface and the single canonical way to retrieve the validity of the token is to retrieve the `Valid` property of the `Token` struct.
* The previous fact was enhanced by the fact that most claims implementations had additional exported `VerifyXXX` functions, which are now removed
* All validation errors should be comparable with `errors.Is` to determine, why a particular validation has failed
* Developers want to adjust validation options. Popular options include:
* Leeway when processing exp, nbf, iat
* Not verifying `iat`, since this is actually just an informational claim. When purely looking at the standard, this should probably the default
* Verifying `aud` by default, which actually the standard sort of demands. We need to see how strong we want to enforce this
* Developers want to create their own claim types, mostly by embedding one of the existing types such as `RegisteredClaims`.
* Sometimes there is the need to further tweak the validation of a token by checking the value of a custom claim. Previously, this was possibly by overriding `Valid`. However, this was error-prone, e.g., if the original `Valid` was not called. Therefore, we should provide an easy way for *additional* checks, without by-passing the necessary validations
This leads to the following two major changes:
* The `Claims` interface now represents a set of functions that return the mandatory claims represented in a token, rather than just a `Valid` function. This is also more semantically correct.
* All validation tasks are offloaded to a new (optional) `Validator`, which can also be configured with appropriate options. If no custom validator was supplied, a default one is used.
This PR removes the old legacy standard claims, which have been deprecated since the beginning of the `v4` module in favor of the newer `RegisteredClaims`. Removing them before any further changes to the validation API is quite useful, as less code needs to be adapated.
This PR aims at implementing compliance to RFC7519, as documented in #11 without breaking the public API. It creates a new struct `RegisteredClaims` and deprecates (but not removes) the `StandardClaims`. It introduces a new type `NumericDate`, which represents a JSON numeric date value as specified in the RFC. This allows us to handle float as well as int-based time fields in `aud`, `exp` and `nbf`. Additionally, it introduces the type `StringArray`, which is basically a wrapper around `[]string` to deal with the oddities of the JWT `aud` field.
* Fix issue with MapClaims VerifyAudience []string
There was an issue in MapClaims's VerifyAudiance where a []string (which
is valid in the spec) would return true (claim is found, or nil) when required
was not set.
It now checks interface types correctly and has tests written
Signed-off-by: Alistair Hey <alistair@heyal.co.uk>
* Keep aud validation constant time compare
Keep aud validation using constant time compare by not instantly
returning on a true comparison, keep comparing all options and store
result in a variable
Signed-off-by: Alistair Hey <alistair@heyal.co.uk>
Co-authored-by: Banse, Christian <christian.banse@aisec.fraunhofer.de>
Christian Banse