In the scenario of knocking on the door of an apartment with suspected drug trafficking, which principle supports the legality of the search conducted after permission was granted?

The concept of actual authority is the correct principle that supports the legality of the search conducted after permission was granted. Actual authority refers to the power that an individual has to grant permission for a search based on their rights to control or access a space. In the context of a suspected drug trafficking situation, if the person who answered the door had the legal right to consent to the search—meaning they were an occupant or had the owner's permission—then any evidence discovered during that search is typically considered admissible in court.

Permission must be informed and voluntary, but if granted by someone with actual authority over the premises, it legitimizes the search. This principle is grounded in legal precedents which emphasize the rights of individuals in possession or control of property to allow law enforcement access.

Other options involve different aspects of authority that may not necessarily pertain to the specific scenario where actual permission is clear and obtained. The landlord/tenant authority could imply existing dynamics in legal relationships that may not confer the ability to grant consent effectively, while common authority refers to situations where multiple individuals share control over a space. The argument about legality being rejected does not apply when actual authority is established, highlighting the importance of the correct understanding of legal consent in search scenarios.