Test with FIPS

[jeroen]

On CentOS we can set an envvar OPENSSL_FORCE_FIPS_MODE=1 to enable FIPS.
See #95

[jeroen]

Added fips_mode() api: bcdf9dd

[atheriel]

I have a patch that allows the test suite to run on a FIPS system. Should I submit it to help with this issue?

[jeroen]

Sure, I made a start by skipping some tests. But it looks like there are some are actual bugs, where openssl is refusing an operation in places that I did not anticipate. I just saw an error negative length vectors are not allowed which probably means that I am somewhere treating an error code -1 as an actual result and trying to copy that into an R vector.

[atheriel]

I think I fixed those, let me verify and submit.

[jeroen]

Btw, do you have access to the rstudio cloud revdep checker? It would be good if we can identify if the changes broke any R packages.

[atheriel]

@jeroen I think the answer is "yes". Can you let me know which commit you'd like me to run it against?