The Oakland Raiders entered this offseason with upwards of $70 million in salary cap space and a mandate to spend at least $41 million of it to reach the NFL's required salary floor. But unlike previous seasons in which the Raiders had oodles of cap space and no one to spend it on, free agents actually wanted to come to Oakland this time around.

General manager Reggie McKenzie has done a good job building an impressive young nucleus consisting of Derek Carr, Khalil Mack and Amari Cooper. With those three difference makers in place, free agents are looking at the Raiders in a whole new light. That's why McKenzie was able to address a few key needs in free agency so far by signing offensive lineman Kelechi Osemele, pass rusher Bruce Irvin and cornerback Sean Smith.

But I'm still concerned with Oakland's secondary. Smith has allowed fewer than 60 percent of passes thrown at him to be caught in every season of his career. He will provide an immediate upgrade over McKenzie's first pick as Raiders GM D.J. Hayden, who has disappointed as a first-rounder. And while midseason CB pickup David Amerson helped out last year, the Raiders still finished the 2015 season ranked No. 26 in passing yards allowed per game (259), No. 15 in passing touchdowns allowed (25) and No. 16 in opposing completion percentage (63.0).

Finding a No. 1 cornerback of the future should be a priority heading into the 2016 NFL Draft. Lucky for McKenzie and the Raiders, there are two enticing options that could be available when Oakland picks at No. 14.

Ohio State's Eli Apple is a name that has been linked with the Raiders before. Apple is a natural cover corner with fluid hips that allow him to change direction quickly. He also possesses fast hands that enable him to make plays on the ball. The accomplished CB was voted the Defensive MVP of Ohio State's Fiesta Bowl win over Notre Dame. With good size and speed, he has been compared to Trumaine Johnson.

Mackensie Alexander is another guy who should be on Oakland's radar. Though just a redshirt sophomore, Alexander boasts a ton of raw talent and an intriguing upside. There may be some growing pains in Year 1, but Alexander could turn into a shutdown corner given time. With his competitive nature and strong play, he's drawn comparisons to Desmond Trufant.

Yes, the Raiders have needs elsewhere on the roster. But it would be difficult for McKenzie to pass up the opportunity to solidify Oakland's pass defense for years to come. 

For more, follow Brandon Katz on Twitter: @Great_Katzby