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