libcamera: pub_key: Support openssl as an alternative to gnutls

Support verify IPA signatures with openssl as an alternative to gnutls,
to offer more flexibility in the selection of dependencies. Use gnutls
by default, for no specific reason as both are equally well supported.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/meson.build

@@ -65,12 +65,16 @@ subdir('pipeline')
 subdir('proxy')
 
 libdl = cc.find_library('dl')
-libgnutls = dependency('gnutls', required : true)
 libudev = dependency('libudev', required : false)
 libyaml = dependency('yaml-0.1', required : false)
 
-if libgnutls.found()
+# Use one of gnutls or libcrypto (provided by OpenSSL), trying gnutls first.
+libcrypto = dependency('gnutls', required : false)
+if libcrypto.found()
     config_h.set('HAVE_GNUTLS', 1)
+else
+    libcrypto = dependency('libcrypto', required : true)
+    config_h.set('HAVE_CRYPTO', 1)
 endif
 
 if liblttng.found()
@@ -135,8 +139,8 @@ libcamera_deps = [
     libatomic,
     libcamera_base,
     libcamera_base_private,
+    libcrypto,
     libdl,
-    libgnutls,
     liblttng,
     libudev,
     libyaml,