Empty exception when parsing Go paseto v2 public

[hazcod]

Hi! Thank you for the library.

I am trying to parse a public (v2) paseto token generated by https://github.com/o1egl/paseto .
However, an empty exception is returned when parsing.

        try:
            parsed = paseto.parse(
                key=self.tokenSecretKey,
                purpose='local',
                token=tokenValue,
                encoder=paseto.JsonEncoder, 
                validate=False,
                rules=None,
                required_claims=[
                    '1',
                    '2',
                    '3',
                ]
            )
        except Exception as e:
            raise ValueError("token decrypt failed: " + str(e))

Returns: token decrypt failed:.

Generator:

			now := time.Now()
                        pasetoV2 := paseto.NewV2()
			jsonToken := paseto.JSONToken{
				Audience:   "",
				Subject:    "",
				Issuer:     "foo",
				Jti:        strconv.FormatUint(ID, 10),
				Expiration: now.AddDate(0, 0, tokenExpiryDays),
				IssuedAt:   now,
				NotBefore:  now,
			}

			jsonToken.Set("1", testUUID)
			jsonToken.Set("2", strconv.FormatUint(ID, 10))
			jsonToken.Set("3", user.Name)

			token, err := pasetoV2.Encrypt(cryptoKeyBytes, jsonToken, nil)
			if err != nil { ... }

[rlittlefield]

If you have a public token, try passing in purpose='public' to the paseto.parse call. If you pass "local", it will be expecting a local type token.

[rlittlefield]

Not sure if you had any luck with this. I'm guessing this is because we don't have messages for some of these exceptions.

I've added this issue to track this: #18

If you are having trouble figuring out which exception before I get a fix in for this, you can to str(type(e)), which should give you the name of the exception class.