add more bcrypt tests

* check for invalid salt values for all bcrypt variants
* check for valid return value on glibc 2.28

I am not entirely sure this cutoff is correct, but RHEL 8 runs glibc
2.28 and supports bcrypt, and Ubuntu 18.04 Bionic has glibc 2.27 and
does not.  Ubuntu Focal 20.04 has glibc 2.31 and also supports bcrypt.
We will see what the test harness reports :-)

Author: kjetilho

spec/functions/pw_hash_spec.rb

@@ -53,6 +53,9 @@
   context 'when the third argument contains invalid characters' do
     it { is_expected.to run.with_params('password', 'sha-512', 'one%').and_raise_error(ArgumentError, %r{characters in salt must be in the set}) }
     it { is_expected.to run.with_params('password', 'bcrypt', '1234').and_raise_error(ArgumentError, %r{characters in salt must match}) }
+    it { is_expected.to run.with_params('password', 'bcrypt-a', '1234').and_raise_error(ArgumentError, %r{characters in salt must match}) }
+    it { is_expected.to run.with_params('password', 'bcrypt-x', '1234').and_raise_error(ArgumentError, %r{characters in salt must match}) }
+    it { is_expected.to run.with_params('password', 'bcrypt-y', '1234').and_raise_error(ArgumentError, %r{characters in salt must match}) }
   end
 
   context 'when running on a platform with a weak String#crypt implementation' do
@@ -61,6 +64,22 @@
     it { is_expected.to run.with_params('password', 'sha-512', 'salt').and_raise_error(Puppet::ParseError, %r{system does not support enhanced salts}) }
   end
 
+  begin
+    require 'etc'
+    if Etc.confstr(Etc::CS_GNU_LIBC_VERSION) =~ %r{(\d+)\.(\d+)} and $1.to_i > 2 or ($1.to_i == 2 and $2.to_i >= 28)
+      context 'when running on platform with bcrypt' do
+        it { is_expected.to run.with_params('password', 'bcrypt', '05$salt.salt.salt.salt.sa').and_return('$2b$05$salt.salt.salt.salt.sO5QUgeeLRANZyvfNiKJW5amLo3cVD8nW') }
+        it { is_expected.to run.with_params('password', 'bcrypt-a', '05$salt.salt.salt.salt.sa').and_return('$2a$05$salt.salt.salt.salt.sO5QUgeeLRANZyvfNiKJW5amLo3cVD8nW') }
+        it { is_expected.to run.with_params('password', 'bcrypt-x', '05$salt.salt.salt.salt.sa').and_return('$2x$05$salt.salt.salt.salt.sO5QUgeeLRANZyvfNiKJW5amLo3cVD8nW') }
+        it { is_expected.to run.with_params('password', 'bcrypt-y', '05$salt.salt.salt.salt.sa').and_return('$2y$05$salt.salt.salt.salt.sO5QUgeeLRANZyvfNiKJW5amLo3cVD8nW') }
+      end
+    else
+      pending("Only testing bcrypt results on glibc 2.28 and later")
+    end
+  rescue NameError
+    pending("Only testing bcrypt results on glibc")
+  end
+
   if RUBY_PLATFORM == 'java' || 'test'.crypt('$1$1') == '$1$1$Bp8CU9Oujr9SSEw53WV6G.'
     describe 'on systems with enhanced salts support' do
       it { is_expected.to run.with_params('password', 'md5', 'salt').and_return('$1$salt$qJH7.N4xYta3aEG/dfqo/0') }