Remove dependency on conmmons-codec by using java.util.Base64

[j3graham]

see gh-11318

First commit removes test usages of Base64 and some other minor commons-codec functions.

[rwinch]

Thanks for the PR @j3graham To start, I think another change might be to remove commons-codec occurences from *.gradle files so the dependency is no longer added to the classpath.

rg commons-codec
messaging/spring-security-messaging.gradle
18:	testImplementation 'commons-codec:commons-codec'

build.gradle
92:			components.withModule("commons-codec:commons-codec") { selection ->
95:					selection.reject("commons-codec updates break saml tests");

web/spring-security-web.gradle
23:	testImplementation 'commons-codec:commons-codec'

dependencies/spring-security-dependencies.gradle
26:		api "commons-codec:commons-codec:1.15"

I'll leave it to @jzheaux to review this further.

[j3graham]

Dependencies removed.

[jzheaux]

Thanks, @j3graham! I've left some feedback inline.

[jzheaux]

Also, would you please consider rebasing this PR on 5.8.x so that the enhancement can get out to folks a little sooner?

[j3graham]

Will be happy to rebase it when you're happy with this version. Interestingly the minor StandardCharsets change you called out requires Java 10, so will need to leave that out.

[j3graham]

New PR for 5.8.x: #11322

javax->jakarta changes were a bit awkward.

Perhaps we can abandon this one in favour of the 5.8.x one and let the merge to main happen.

[j3graham]

@jzheaux Should I fix up this PR, or will the one from 5.8 get merged independently?

[jzheaux]

Because of javax->jakarta, the merge isn't clean so it needs to be done manually. Since you've done that work already, I figure we can finish this PR, too. That said, if you are out of time, I can take care of it by cherry-picking the other and changing the package names.

Up to you -- if you close the PR, I'll do the cherry-picking. If not, we can merge this one as well once it's ready.

[j3graham]

I cherry-picked the change and fixed the jakarta stuff.