Meaning of "leave to be allowed to write it anonymously"

When Mr. Ashley Sampson suggested to me the writing of this book, I asked leave to be allowed to write it anonymously, since, if I were to say what I really thought about pain, I should be forced to make statements of such apparent fortitude that they would become ridiculous if anyone knew who made them.

What does it mean leave to be allowed to write it anonymously mean?

leave noun
Definition of leave (Entry 2 of 3)
1a: permission to do something

https://www.merriam-webster.com/dictionary/leave

Here, it's a bit redundant, as "leave" and "be allowed" both mean to have permission.

Also, the hyphen in "writing" was probably there because the word straddled two lines in the original text. Now that you're quoting it and it is all on one line (at least, in the rendering for my browser's settings), the hyphen should not be included.