Use strict base64 encoding (no newline)

[lloeki]

2.0 Upgrade Guide notes

What does this PR do?

Use strict base64 encoding.

Motivation:

MIME-style newlines in the middle of base64 makes for some unhappy results.

Additional Notes:

Reported case was with compressed data on appsec derivative results (e.g schema), introduced in 8c52213

This also applies to a few areas like RC capabilities, although the contents was smaller thus not affected (a trailing newline was handled with a chomp.

How to test the change?

CI covers it (added a non-regression test)

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[ivoanjo]

👍 LGTM

I wonder if we should introduce a helper method for this -- not to avoid repeating code (it's one line), but because we wouldn't have to keep "remembering" to use the correct variant of base64 (although we'd need to remember to use the helper ;D )

[lloeki]

we wouldn't have to keep "remembering" to use the correct variant of base64

The correct version depends on what you're doing. It just turns out that the changes here all use the non-MIME one but it's really a case by case.

(although we'd need to remember to use the helper ;D )

So true. It's also less explicit, hiding the fact that should be in plain sight and in context.