The most common and most likely answer to this crossword clue is the 10 letter word PERMISSIVE
I've seen this crossword clue in The Daily Telegraph
P
E
R
M
I
S
S
I
V
E
More clues leading to the result PERMISSIVE
- Free agent returned letter
- Each letter is liberal
- A letter for free
- King on record over letter granting liberty
- A letter granting authorisation
- Liberal agent brought back message
- For each error the compiler’s tolerant
- A girl I have that’s free with favours
- Impressive spin from Liberal
- Authorizing each letter
Buddy explains!

The straight part
We know that "granting authorisation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case granting authorisation = permissive.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 PERMISSIVE mean?
PERMISSIVE adjective- Giving permission, or predisposed to give it; lenient
- (of a footpath) open to the public by permission of the landowner
- That allows the replication of viruses