What gives me the right to search a vehicle after my K9 alerts to it?

Once LE has probable cause, the person, place or thing can be searched. However, a warrant is required to search if there is no exception. Step one, an alert/final indication is probable cause. The United States Supreme Court in Florida v. Harris (2013) 568 U.S. 237, 243-250, upheld a warrantless search of a vehicle because a K9 sniff constituted probable cause. Step two, no warrant is needed because of the automobile exception. See United States v. Ross (1982) 456 U.S. 798, for example. So, once a properly trained K9 alerts on a vehicle for controlled substances, that provides probable cause to search for all contraband on which the K9 is trained and LE can search that vehicle without a warrant.