Service A exchanges messages with Service B multiple times during the same runtime service activity. Communication between Services A and B has been secured using transport-layer security. With each service request message sent to Service B (1A. IB), Service A includes an X.509 certificate, signed by an external Certificate Authority (CA).
Service B validates the certificate by retrieving the public key of the CA (2A. 2B) and verifying the digital signature of the X.509 certificate. Service B then performs a certificate revocation check against a separate external CA repository (3A, 3B). No intermediary service agents reside between Service A and Service B.

Service B has recently suffered from poor runtime performance plus it has been the victim of an access-oriented attack. As a result, its security architecture must be changed to fulfill the following new requirements: 1. The performance of security-related processing carried out by Service B when communicating with Service A must be improved. 2. All request messages sent from Service A to Service B must be screened to ensure that they do not contain malicious content.
Which of the following statements describes a solution that fulfills these requirements?

• A. Apply the Trusted Subsystem pattern to by introducing a new utility service. Because Service B is required to limit the use of external resources. Service A must ensure that no other services can request processing from Service B in order to prevent malicious content from infiltrating messages. This is achieved by creating a dedicated replica of Service B to be used by the utility service only. Upon receiving the request message and the accompanying security credentials from Service A.
  the utility service verifies the authentication information and the validity of the X.509 signature. If the authentication information is correct, then the utility service replicates the code of Service B, performs the necessary processing, and returns the response to Service A.
• B. Eliminate the need to retrieve the public key from the Certificate Authority and to verify the certificate revocation information by extending the service contract of Service B to accept certificates only from pre-registered Certificate Authorities. This form of pre- registration ensures that Service B has the public key of the corresponding Certificate Authority.
• C. Apply the Trusted Subsystem pattern by introducing a new utility service between Service A and Service B.
  When Service A sends request messages, the utility service verifies the provided credentials and creates a customized security profile for Service A.
  The security profile contains authentication and access control statements that are then inherited by all subsequent request messages issued by Service A.
  As a result, performance is improved because Service A does not need to resubmit any additional credentials during subsequent message exchanged as part of the same runtime service activity. Furthermore, the utility service performs message screening logic to filter out malicious content.
• D. Add a service agent to screen messages sent from Service A to Service B.
  The service agent can reject any message containing malicious content so that only verified messages are passed through to Service B.
  Instead of using X.509 certificates, use WS- SecureConversation sessions. Service A can request a Security Context Token (SCT) from a Security Token Service and use the derived keys from the session key to secure communication with Service B.
  Service B retrieves the session key from the Security Token Service.

Service Consumer A sends a request message with a Username token to Service A (1).
Service B authenticates the request by verifying the security credentials from the Username token with a shared identity store (2), To process Service Consumer A's request message. Service A must use Services B, C, and D.
Each of these three services also requires the Username token (3. 6, 9) in order to authenticate Service Consumer A by using the same shared identity store (4, 7, 10). Upon each successful authentication, each of the three services (B, C, and D) issues a response message back to Service A (5, 8, 11).
Upon receiving and processing the data in all three response messages, Service A sends its own response message to Service Consumer A (12).

There are plans implement a single sign-on security mechanism in this service composition architecture. The service contracts for Services A, C, and D can be modified with minimal impact in order to provide support for the additional messaging requirements of the single sign-on mechanism. However, Service B's service contract is tightly coupled to its implementation and, as a result, this type of change to its service contract is not possible as it would require too many modifications to the underlying service implementation.
Given the fact that Service B's service contract cannot be changed to support single sign- on, how can a single sign-on mechanism still be implemented across all services?

• A. Replace the Username tokens with X.509 digital certificates. This allows for the single sign-on mechanism to be implemented without requiring changes to any of the service contracts.
• B. Apply the Brokered Authentication pattern to establish Service A as an authentication broker that issues a SAML token for Service Consumer A and forwards Service Consumer A's token to other services. Apply the Trusted Subsystem pattern to create a utility service that acts as a trusted subsystem for Service B.
  This utility service is able to perform authentication using the SAML token from Service A and can then generate a Username token by embedding its own credentials when accessing Service B.
  This way, Service B can perform authentication of request messages as it does now, but it can still participate in the single sign-on message exchanges without requiring changes to its service contract.
• C. Apply the Brokered Authentication pattern so that Service A acts as an authentication broker that issues a SAML token for Service Consumer A and forwards Service Consumer A's token to Services C and D.
  Create a second service contract for Service B that supports single sign-on. This way, Service B can still perform authentication of incoming requests using the old service contract while allowing for the processing of SAML tokens using the new service contract.
• D. Apply the Brokered Authentication pattern so that Service A acts as an authentication broker that issues a SAML token on behalf of Service Consumer A, and forwards this token to Services C and D.
  Create a new utility service is positioned between Service A and Service B.
  This utility service perform a conversion of the SAML token to a Username token, and then forwards the Username token to Service B so that Service B can still perform authentication of incoming requests using its own security mechanism.