@Nullable
    public String tokenType() {
        return tokenType;
    }
{@value OAuth2Constants#TOKEN_TYPE} Token Introspection Response field,
OPTIONAL. Type of the token as defined at
<a href="https://datatracker.ietf.org/doc/html/rfc6749#section-7.1">[RFC6749], Section 7.1</a>.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/OAuth2TokenDescriptor.java