The phrase "authentic key" is correct and usable in written English.
It can be used in contexts where you want to emphasize the genuineness or originality of a key, whether literal or metaphorical.
Example: "To access the secure area, you must use the authentic key provided by the security team."
Alternatives: "genuine key" or "original key".
Served with corn, coleslaw or greens from another neighborhood outfit, Added Value farm across the street from Ikea (and Key lime pie from the neighborhood tough-guy Steve Tarpin of Steve's Authentic Key Lime Pies on Pier 41 for dessert), it's money well spent for a kind of neighborhood feeling that generally doesn't take in New York City.
Then a stop to try Steve's Authentic Key Lime Pies.
STEVE'S AUTHENTIC KEY LIME PIES Pies to take home, with single-servings on site.
Tastings, daily, start at $5. Steve's Authentic Key Lime Pies Steve Tarpin is a pioneer's pioneer.
Shannon ended the Red Hook tour at Steve's Authentic Key Lime Pies.
The Swingle is sold only at its fount of origin, Steve's Authentic Key Lime Pies, in Red Hook, Brooklyn.
As the youngest president in the Harvard Alumni Association's modern history, Wang believes being authentic is key to deeper engagement across the alumni community.
In addition to a tight sense of verisimilitude (performances from a straight-faced cast are wonderfully authentic) several key segments were staged at real-life events, including the Melbourne Cup and a the industry's biggest event, the Pumper and Cleaner Expo in Nashville, Tennessee, dubbed "Poo HQ" by Kenny.
I believe being authentic is key, too.
Many say that being authentic is key, but like I showed in the Kardashian example above, we don't prefer people who share every aspect of their life, which may be truly the authentic them.
El Molino, known for its street food and tamales, offers authentic flavors keyed to the seasons.
