Final answer:
Using someone else's credentials to access a door or system is a form of identity theft or true-name fraud, involving wrongful acquisition and use of personal information to commit fraud.
Step-by-step explanation:
The act of using someone else's credentials to gain access to a door or system without their permission is referred to as identity theft, more specifically indicated in the context you are referring to could be called credential misuse or unauthorized access. Identity theft, or true-name fraud, involves wrongfully acquiring and using another person's personal identification, credit, or account information. This information, such as a social security number, pin number, or password, is then used to commit various fraudulent activities, which could include draining the victim's savings accounts or making expensive purchases like automobiles, boats, and jewelry.