MC Trade has a full API and can be set up to integrate with other systems for the purpose of Single Sign On (SSO), a process by which a 3rd party software can validate access from your MC Trade system and pass that permission over to a 3rd party software.
Depending on what system you want to integrate, the technical details will change on how that Single Sign On is built. If you are planning to work with another system who wants to create a Single Sign On process with MC Trade, please make sure to send them to this documentation: http://developers.weblinkconnect.com/api-v1/api-authorization
Note, creating a SSO process requires the use of the MC Trade API, which may incur an added charge to your annual subscription.