Wrap errors with %w instead of %v

[d10i]

Description

Wrap errors using %w instead of %v. This allows handling errors based on the internal errors with errors.Is and errors.As, as explained here. This feature has been introduced in Go 1.13 and is back-compatible and as this repo already uses Go 1.14 it should not introduce breaking changes.

This allows returning different error types in the ValidationKeyGetter function and then use them in the error returned by CheckJWT. For example:

type MyCustomError struct {
	error       string
	serverError bool
}

// Implement error interface
func (e MyCustomError) Error() string {
	return e.error
}

func main() {
	mw := jwtmiddleware.New(jwtmiddleware.Options{
		ErrorHandler: func(w http.ResponseWriter, r *http.Request, err string) {
			// ...
		},
		ValidationKeyGetter: func(token *jwt.Token) (interface{}, error) {
			if somethingUnexpectedHappened() {
				return nil, MyCustomError{error: "Server error", serverError: true}
			}

			if badRequest() {
				return nil, MyCustomError{error: "Bad request", serverError: false}
			}

			// ...

			return publicKey, nil
		},
		SigningMethod: jwt.SigningMethodRS256,
	})

	err := mw.CheckJWT(...)
	if err != nil {
		var myCustomError MyCustomError
		
		if errors.As(err, &myCustomError) {
			if myCustomError.serverError {
				// Return HTTP 500 Internal Server Error
			}

			// Return HTTP 401 Unauthorized
		}

		// Default: Return HTTP 500 Internal Server Error
	}
}

References

• Working with Errors in Go 1.13: https://blog.golang.org/go1.13-errors

Testing

No tests have been added because:

• There doesn't currently seem to be tests testing this low-level type of thing at the moment.

• It's non-breaking change that doesn't change the behaviour, unless errors.Is or errors.As are used.

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[grounded042]

Great change. Thanks @d10i!