public String rawResponse() {
        if (rawResponse == null) {
            // WARNING: do not include {@code issuedAt()} to the raw response
            // as {@code issuedAt()} is a derived field and it's not part of the OAuth2 server response
            rawResponse = composeRawResponse(accessToken, tokenType,
                                             null, expiresIn, refreshToken, scope, extras);
        }
        return rawResponse;
    }
{@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