@Override
    public String toString() {
        if (toString == null) {
            // include {@code issuedAt()} to toString()
            toString = composeRawResponse(accessToken, tokenType, issuedAt, expiresIn,
                                          refreshToken, scope, extras);
        }
        return toString;
    }
{@code JSON}-formatted raw Token Introspection Response body. If the {@link GrantedOAuth2AccessToken} was
not parsed out of the raw response body, this value calculated based on the other
{@link GrantedOAuth2AccessToken} values.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/GrantedOAuth2AccessToken.java