I am trying to create some auth functions in Go. I will receive multiple auth types, and different auth types share some utils functions and need to behave slightly differently in those utils functions. I want to use sub-functions to achieve these differences to reduce duplicates.

For example, all auth types share validate_token function, however inside validate_token function, I need a parse_token function which behaves differently according to the auth type.

The below codes are how I am trying to approach this, but I get error: panic: runtime error: invalid memory address or nil pointer dereference in testing. When I change func (m authType1) parse_token to func (m auth) parse_token and call the parse_token function by m.parse_token, the error goes away (But I do need parse_token to be different according to different auth types).

Does anyone know how I should fix these codes? Thanks a lot!

type auth struct {
    config  AuthConfig
}

type authType1 struct {
    auth
}

type authType2 struct {
    auth
}

type parseToken interface {
    parse_token(token *oauth2.Token) (*jwt.Token, error)
}

func (m auth) validateToken(token *oauth2.Token, f parseToken) (*jwt.Token, error) {
    ...
    jwtToken, err := f.parse_token(token)
    return jwtToken, err
}

func (m authType1) parse_token(token *oauth2.Token) (*jwt.Token, error) {
    ...
}

func (m authType2) parse_token(token *oauth2.Token) (*jwt.Token, error) {
    ...
}