creds: Add ImportCredential=

ImportCredential= takes a credential name and searches for a matching
credential in all the credential stores we know about it. It supports
globs which are expanded so that all matching credentials are loaded.

test/units/testsuite-54.sh

@@ -253,6 +253,21 @@ cmp /tmp/ts54-concat <(echo -n abcd)
 rm /tmp/ts54-concat
 rm -rf /tmp/ts54-creds
 
+# Check that globs work as expected
+mkdir -p /run/credstore
+echo -n a >/run/credstore/test.creds.first
+echo -n b >/run/credstore/test.creds.second
+mkdir -p /etc/credstore
+echo -n c >/etc/credstore/test.creds.third
+systemd-run -p "ImportCredential=test.creds.*" \
+            -p DynamicUser=1 \
+            --wait \
+            --pipe \
+            cat '${CREDENTIALS_DIRECTORY}/test.creds.first' \
+                '${CREDENTIALS_DIRECTORY}/test.creds.second' \
+                '${CREDENTIALS_DIRECTORY}/test.creds.third' >/tmp/ts54-concat
+cmp /tmp/ts54-concat <(echo -n abc)
+
 # Now test encrypted credentials (only supported when built with OpenSSL though)
 if systemctl --version | grep -q -- +OPENSSL ; then
     echo -n $RANDOM >/tmp/test-54-plaintext