doh: use https protocol by default

The only allowed protocol is https, so it makes sense to use that
by default if not passed explicitly by the user.

Reported-by: MasterInQuestion on github
Reviewed-by: Jay Satiro
Fixes #9163
Closes #9165

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/doh.c b/lib/doh.c
index a21c94f88..a86e157fc 100644
--- a/lib/doh.c
+++ b/lib/doh.c
@@ -243,6 +243,7 @@ static CURLcode dohprobe(struct Curl_easy *data,
        the gcc typecheck helpers */
     struct dynbuf *resp = &p->serverdoh;
     ERROR_CHECK_SETOPT(CURLOPT_URL, url);
+    ERROR_CHECK_SETOPT(CURLOPT_DEFAULT_PROTOCOL, "https");
     ERROR_CHECK_SETOPT(CURLOPT_WRITEFUNCTION, doh_write_cb);
     ERROR_CHECK_SETOPT(CURLOPT_WRITEDATA, resp);
     ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDS, p->dohbuffer);