presto-spi/src/main/java/io/prestosql/spi/security/Identity.java/Identity/toString
class Identity:    @Override
    public String toString()
    {
        StringBuilder sb = new StringBuilder("Identity{");
        sb.append("user='").append(user).append('\'');
        principal.ifPresent(principal -> sb.append(", principal=").append(principal));
        sb.append(", roles=").append(roles);
        sb.append(", extraCredentials=").append(extraCredentials.keySet());
        sb.append('}');
        return sb.toString();
    }