public OAuth2TokenDescriptorBuilder tokenType(String tokenType) {
        this.tokenType = requireNonNull(tokenType, "tokenType");
        return this;
    }
{@code 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/OAuth2TokenDescriptorBuilder.java