It contains everything needed for
https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/private-content-signed-urls.html#private-content-how-signed-urls-work
except for the key id

we also reduce the number of tests to 1/10th due to the signing
computation required.

Ref:
https://github.com/varnishcache/varnish-cache/commit/681c11998ec56dc4460a30585210f95a7850ea3b

This enables definition of keys where the PEM form is not evailable,
for example from JSON Web Key (JWK) files.

Ref: https://tools.ietf.org/html/rfc7517#section-9.3

The full suite is still available via a Makefile.am modification

Ref: https://github.com/varnishcache/varnish-cache/commit/5450550906d0809dfc21ae9d3a5b14446c1809d4

ref: 0c74d1b99f1f43fc99725fe14322760afa7858ee

This reverts commit a38d3232.