The most common and most likely answer to this crossword clue is the 5 letter word LOGON
L
O
G
O
N
Buddy explains!
The straight part
We know that "Gaining access with code" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gaining access with code = logon.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LOGON mean?
LOGON noun- A combination of a user's identification and password used to enter a computer.
- The process of logging on.