public GrantedOAuth2AccessTokenBuilder issuedAt(Instant issuedAt) {
        this.issuedAt = requireNonNull(issuedAt, "issuedAt");
        return this;
    }
An {@link Instant} indicating when the Access Token was issued,
OPTIONAL. The value is NOT supplied with the Access Token response and calculated approximately using
{@value OAuth2Constants#EXPIRES_IN} field.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/GrantedOAuth2AccessTokenBuilder.java