Use SHA digests for FIPS compliance

[jonahx]

What does this PR do?

Configures Rails to use SHA instead of md5

What ticket does this PR close?

#1418

Checklists

Change log

• The CHANGELOG has been updated, or
• This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• This PR includes new unit and integration tests to go with the code changes, or
• The changes in this PR do not require tests

Follow-on issues

• Follow-up issue(s) have been logged (and links included below) to update documentation or related projects, or
• No follow-up issues are required

[jvanderhoof]

@jonahx, mind adding a changelog entry for this? Although it shouldn't change outward behavior, users may be interested in the change.

[jtuttle]

Looks fine, though I did find this GH issue: rails/rails#38791

We are calling similar functions in a couple of places:

~/work/conjur (ruby-2.5.1@conjur-evoke) $ ag hexdigest .
app/models/policy_version.rb
96:    self.policy_sha256 = Digest::SHA256.hexdigest(policy_text)

app/models/host_factory_token.rb
29:      where(token_sha256: Digest::SHA256.hexdigest(token)).all.find do |hft|
81:    self.token_sha256 = Digest::SHA256.hexdigest(self.token)

We might want to just confirm that these are covered by CI before merging. If not, they're similar enough to what's discussed in that GH issue that I'd be concerned they may error when actually called.

[jtuttle]

I just checked CodeClimate's coverage data and it says both of the lines I called out above are covered by tests, so I think we're good.

https://codeclimate.com/github/cyberark/conjur/app/models/policy_version.rb/source?to_sha=0cc77db14d552d396dda55ebf33797e0df80e47d

https://codeclimate.com/github/cyberark/conjur/app/models/host_factory_token.rb/source?to_sha=0cc77db14d552d396dda55ebf33797e0df80e47d

[codeclimate]

Code Climate has analyzed commit 601f3c6 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 85.4% (0.0% change).

View more on Code Climate.