Add @FunctionalInterface to AuthenticationManager

[pongdangx2]

AuthgenticationManager Interface is being implemented by using lambda expression.
Therefore, It would be clear not to add more abstract function, If @FunctionalInterface annotation is added.

[jzheaux]

Thanks, @pongdangx2. Will you do me a favor and leave the copyright as-is? The Ageci copyright header is a special case.

[pongdangx2]

Thank you, @jzheaux I just restore the copyright line :)

[jzheaux]

@pongdangx2 will you please also squash your commits? This makes backporting simpler.

It would also be nice if the commit title were capitalized, like so:

Add @FunctionalInterface to AuthenticationManager

[pongdangx2]

@jzheaux
I rebase my commits. And another commit is created, that I didn't make. (commit 06a9227)

Could you please check if I should do something else??or I did right..?

[jzheaux]

Thanks for hanging in there! For the rebase to work, @pongdangx2, you need to rebase to the most recent version of main.

It's easier to do this if you have a branch with your changes. So, first, I'd recommend doing the following:

git checkout -b authentication-manager-functional-interface
git checkout main

Now you have your changes saved to a separate branch and are back on main. Then, you will want to make your main up to date with the Spring Security upstream. For the following, imagine that the name you use locally for your fork is origin and the same of the Spring Security upstream is called spring-projects:

git fetch spring-projects
git reset --hard spring-projects/main
git push origin main

Now main on your fork should be the same as Spring Security. You can verify this by doing:

$> git status
...
Your branch is up to date with 'spring-projects/main'.

Having done this, you can rebase your branch and push it by doing:

git checkout authentication-manager-functional-interface
git rebase main
git push origin authentication-manager-functional-interface

Finally, close this PR and create a new one based on your branch.

While several steps, this approach will save you time later on as you will create a branch the moment you start a new feature or bug fix.