json: cannot unmarshal object into Go value of type jwt.Claims

[rentateamdev1]

https://github.com/dgrijalva/jwt-go/blob/master/parser.go#L131
this decode code always returns decode error
json: cannot unmarshal object into Go value of type jwt.Claims
because claims variable is declared as interface not a struct

[dgrijalva]

jwt.Claims is an interface. The claims value you pass into the parser needs to be a concrete type. It's essentially passed directly through to the standard library JSON parser and will follow that behavior.

[rentateamdev1]

The error is that json decoder could not decode to variable of type Claims, because Claims is an interface and decoder do not know what real type is
I wrote an example of code, based on https://github.com/dgrijalva/jwt-go/blob/master/parser.go#L131

With error: https://play.golang.org/p/WT5yd2X_iCI
Without error: https://play.golang.org/p/2NOnAf267HA

[kheraud]

@rentateamdev1 , use a pointer to your custom claim instead of a value one. An interface is a tuple (concrete type, value). If you use a pointer type (*MyCustomClaim) as the concrete type of your interface, encoding/json figures out the json tags of your struct.

var claims jwt.Claims = &MyCustomClaims{}
...
err := dec.Decode(&claims)

Or for your example with error : claims = &StandardClaims{}

[zhangguanzhang]

I used this is ok

func ParseToken(tokenStr string) (*Claims, error) {
	var claims *Claims
	token, err := jwt.ParseWithClaims(tokenStr, &Claims{}, func(token *jwt.Token) (interface{}, error) {
		return conf.JWTKey(), nil
	})

	if token != nil {
		if claims, ok := token.Claims.(*Claims); ok && token.Valid {
			return claims, nil
		}
	}

	return claims, err
}

[mieubrisse]

I'm not the OP, but @kheraud 's solution fixed this for me. The example for a custom claims type has this same logic, so maybe just a quick explanatory comment on the example could close this issue?