Warn rather than raise on opportunistic auth failure.

When opportunistic_auth is enabled but an Authorization header
could not be generated opportunistically, log a warning rather
than raising an exception. (If the request results in a 401
and we fail to generate an Authorization header in that (no-
longer-opportunistic) case, an exception is still raised.)

Author: twosigmajab

HISTORY.rst

@@ -1,6 +1,15 @@
 History
 =======
 
+Unreleased
+----------
+
+- When opportunistic_auth is enabled but an Authorization header
+  could not be generated opportunistically, log a warning rather
+  than raising an exception. (If the request results in a 401
+  and we fail to generate an Authorization header in that (no-
+  longer-opportunistic) case, an exception is still raised.)
+
 1.2.3: 2021-02-08
 -----------------
 

requests_gssapi/gssapi_.py

@@ -306,14 +306,20 @@ def __call__(self, request):
             # by the 401 handler
             host = urlparse(request.url).hostname
 
-            auth_header = self.generate_request_header(None, host,
-                                                       is_preemptive=True)
-
-            log.debug(
-                "HTTPSPNEGOAuth: Preemptive Authorization header: {0}"
-                .format(auth_header))
-
-            request.headers['Authorization'] = auth_header
+            try:
+                auth_header = self.generate_request_header(None, host,
+                                                           is_preemptive=True)
+            except SPNEGOExchangeError as exc:
+                log.warning(
+                    "HTTPSPNEGOAuth: Opportunistic auth failed with %s ->"
+                    " sending request without adding Authorization header",
+                    exc,
+                )
+            else:
+                log.debug(
+                    "HTTPSPNEGOAuth: Preemptive Authorization header: {0}"
+                    .format(auth_header))
+                request.headers['Authorization'] = auth_header
 
         request.register_hook('response', self.handle_response)
         try: