auth: only ever pick CURLAUTH_BEARER if we *have* a Bearer token

The Bearer authentication was added to cURL 7.61.0, but there is a
problem: if CURLAUTH_ANY is selected, and the server supports multiple
authentication methods including the Bearer method, we strongly prefer
that latter method (only CURLAUTH_NEGOTIATE beats it), and if the Bearer
authentication fails, we will never even try to attempt any other
method.

This is particularly unfortunate when we already know that we do not
have any Bearer token to work with.

Such a scenario happens e.g. when using Git to push to Visual Studio
Team Services (which supports Basic and Bearer authentication among
other methods) and specifying the Personal Access Token directly in the
URL (this aproach is frequently taken by automated builds).

Let's make sure that we have a Bearer token to work with before we
select the Bearer authentication among the available authentication
methods.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Closes #2754

1 files changed, 9 insertions, 4 deletions

diff --git a/lib/http.c b/lib/http.c
index 9bbf59b79..34565590f 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -342,11 +342,11 @@ static CURLcode http_output_bearer(struct connectdata *conn)
  *
  * return TRUE if one was picked
  */
-static bool pickoneauth(struct auth *pick)
+static bool pickoneauth(struct auth *pick, unsigned long mask)
 {
   bool picked;
   /* only deal with authentication we want */
-  unsigned long avail = pick->avail & pick->want;
+  unsigned long avail = pick->avail & pick->want & mask;
   picked = TRUE;
 
   /* The order of these checks is highly relevant, as this will be the order
@@ -508,6 +508,10 @@ CURLcode Curl_http_auth_act(struct connectdata *conn)
   bool pickhost = FALSE;
   bool pickproxy = FALSE;
   CURLcode result = CURLE_OK;
+  unsigned long authmask = ~0ul;
+
+  if(!conn->oauth_bearer)
+    authmask &= (unsigned long)~CURLAUTH_BEARER;
 
   if(100 <= data->req.httpcode && 199 >= data->req.httpcode)
     /* this is a transient response code, ignore */
@@ -519,14 +523,15 @@ CURLcode Curl_http_auth_act(struct connectdata *conn)
   if(conn->bits.user_passwd &&
      ((data->req.httpcode == 401) ||
       (conn->bits.authneg && data->req.httpcode < 300))) {
-    pickhost = pickoneauth(&data->state.authhost);
+    pickhost = pickoneauth(&data->state.authhost, authmask);
     if(!pickhost)
       data->state.authproblem = TRUE;
   }
   if(conn->bits.proxy_user_passwd &&
      ((data->req.httpcode == 407) ||
       (conn->bits.authneg && data->req.httpcode < 300))) {
-    pickproxy = pickoneauth(&data->state.authproxy);
+    pickproxy = pickoneauth(&data->state.authproxy,
+                            authmask & ~CURLAUTH_BEARER);
     if(!pickproxy)
       data->state.authproblem = TRUE;
   }