It’s a common credit building strategy – becoming an authorized user on someone else’s credit card. Whether it’s a parent, a spouse or that one ultra-financially responsible friend in your group, piggybacking on their credit can add years of history to your credit file nearly overnight. No credit checks. No applications. No hard inquiries pulled from your credit report. Just a big, ol’ bump in your borrowing power. “It absolutely can be rocket fuel for somebody’s credit score,” said Matt Schulz, chief consumer finance analyst at LendingTree, which recently studied the authorized-user gambit. And while there are indeed potential rewards, Lending Tree found it runs some risks, too.