A user would never like to enter its data or information in the website if he/she feels that it would be insecure. Any unauthorized access may lead to identity theft which may subsequently lead to dire consequences. So the main problems associated with the website can be named as:
1. Loss of control: The user has to rely on the provider to ensure data security and privacy, resource availability, monitoring of services and resources.
2. Lack of Trust: Trusting a third party requires taking risks. Basically trust and risk are the opposite sides of the same coin. Some monitoring or auditing capabilities would be required to increase the level of trust.
Another key challenge is related to cost. As a general rule, the costs of managing user identities should be as low as possible to ensure a reasonable return on investment in the website.