All applications, including the Composer Playground, use a business network card from their wallet (a file on the local file system) to connect to the network. The card contains the IP address of the network, the participant's name, and their X.509 public key. This information is used by the network to ensure that they can only have rights to perform certain operations against resources in the network. For example, only particular bank employees should be able to authorize a letter of credit.

You can see how these rights are defined for a business network by examining the Access Control List (ACL) for the network. Select AccessControl on the Define tab:

Scroll through the list to see what rights different users have over the different resources in the network. These rules can relate to types or instances, though the former is more common. Spend a little time investigating the ACL rules in this file.