parse jwt tokens in go

To parse JWT tokens in Go, you first need to install a JWT library like "github.com/dgrijalva/jwt-go". Once you have it installed, you can parse a JWT token by following these steps:

1. Define a struct that matches the claims of your JWT token:

main.go
type MyCustomClaims struct {
    UserID   string `json:"user_id"`
    UserName string `json:"user_name"`
    jwt.StandardClaims
}
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2. Parse the JWT token using the jwt.ParseWithClaims function:

main.go
func parseToken(tokenString string) (*MyCustomClaims, error) {
    token, err := jwt.ParseWithClaims(tokenString, &MyCustomClaims{}, func(token *jwt.Token) (interface{}, error) {
        return []byte("my-secret-key"), nil
    })

    if err != nil {
        return nil, err
    }

    if claims, ok := token.Claims.(*MyCustomClaims); ok && token.Valid {
        return claims, nil
    } else {
        return nil, errors.New("invalid token")
    }
}
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In the above code, we are passing the token string and a struct that matches the claims of the JWT token as arguments to jwt.ParseWithClaims(). Additionally, we define a callback function that is used to verify the signature of the JWT token. In this example, we are using a secret key to sign and verify the JWT token.

If the JWT token is valid, we can then access the claims of the token by casting token.Claims to our custom MyCustomClaims struct.

Note: It's important to use a secure method to store your JWT secret key.