core: teach LoadCredential= to load from a directory

test/units/testsuite-54.sh

@@ -28,8 +28,25 @@ systemd-run -p LoadCredential=passwd:/etc/passwd \
             rm '${CREDENTIALS_DIRECTORY}/passwd' \
     && { echo 'unexpected success'; exit 1; }
 
-# Now test encrypted credentials (only supported when built with OpenSSL though)
+# Check directory-based loading
+mkdir -p /tmp/ts54-creds/sub
+echo -n a >/tmp/ts54-creds/foo
+echo -n b >/tmp/ts54-creds/bar
+echo -n c >/tmp/ts54-creds/baz
+echo -n d >/tmp/ts54-creds/sub/qux
+systemd-run -p LoadCredential=cred:/tmp/ts54-creds \
+            -p DynamicUser=1 \
+            --wait \
+            --pipe \
+            cat '${CREDENTIALS_DIRECTORY}/cred_foo' \
+                '${CREDENTIALS_DIRECTORY}/cred_bar' \
+                '${CREDENTIALS_DIRECTORY}/cred_baz' \
+                '${CREDENTIALS_DIRECTORY}/cred_sub_qux' >/tmp/ts54-concat
+( echo -n abcd ) | cmp /tmp/ts54-concat
+rm /tmp/ts54-concat
+rm -rf /tmp/ts54-creds
 
+# 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
     systemd-creds encrypt --name=test-54 /tmp/test-54-plaintext /tmp/test-54-ciphertext