WebTestClientRequestConverter mishandles cookies whose value contains =

[config25]

WebTestClientRequestConverter.createRequestCookie() uses split("=") to
parse cookie headers. This causes two problems:

• Cookie values containing = (e.g. Base64-padded values like YWJjZGVm==)
  are silently truncated at the first =
• Cookie headers without = throw ArrayIndexOutOfBoundsException

Replace split("=") with indexOf('=') to split on only the first = and
handle the no-= case by returning an empty value.

Fixes gh-1038

base branch 3.0.x

[wilkinsona]

This method has to be public as the 3.0.x branch uses JUnit 4.

[config25]

Sorry about that, I missed the JUnit 4 requirement on the 3.0.x branch. Both test methods are now public. Thank you for catching this!

[wilkinsona]

I don't think this is correct. To have an empty-string value, I believe the header's value would have to be malformed=. Without the equals sign, there should be no cookie at all as the header is invalid. I think failing in this case is fine so I'd just remove lines 108-110.

[config25]

Thanks for the review! I've removed lines 108-110 as suggested.

Since the malformed cookie test (requestWithMalformedCookieHeaderWithoutEqualsSign)
was testing the exact behavior that's now removed, I've also deleted it — failing
in that case is now the expected behavior, as you mentioned.