Do not require authentication for GET requests

Fixes #40.

Signed-off-by: Ivan Shapovalov <intelfx@intelfx.name>

Author: intelfx

README.rst

@@ -90,8 +90,8 @@ settings are **required**:
 
       https://patchwork.ozlabs.org/project/{project_name}/list/
 
-You also require authentication - you can use either API tokens or a
-username/password combination:
+For read-write access, you also need authentication - you can use either API
+tokens or a username/password combination:
 
 ``pw.token``
   The API token for your Patchwork account.
@@ -102,6 +102,8 @@ username/password combination:
 ``pw.password``
   The password for your Patchwork account.
 
+If only read-only access is desired, credentials can be omitted.
+
 The following settings are **optional** and may need to be set depending on
 your Patchwork instance's configuration:
 

git_pw/api.py

@@ -47,16 +47,18 @@ def _token_auth_str(token):  # type: (str) -> str
         return 'Token {}'.format(token.strip())
 
 
-def _get_auth():  # type: () -> requests.auth.AuthBase
+def _get_auth(optional=False):
+    # type: (bool) -> Optional[requests.auth.AuthBase]
     if CONF.token:
         return HTTPTokenAuth(CONF.token)
     elif CONF.username and CONF.password:
         return requests.auth.HTTPBasicAuth(CONF.username, CONF.password)
-    else:
+    elif not optional:
         LOG.error('Authentication information missing')
         LOG.error('You must configure authentication via git-config or via '
                   '--token or --username, --password')
         sys.exit(1)
+    return None
 
 
 def _get_headers():  # type: () -> Dict[str, str]
@@ -136,8 +138,8 @@ def _get(url, params=None, stream=False):
         # 'params' (namely a list of tuples) but it doesn't seem possible to
         # indicate this
         rsp = requests.get(
-            url, auth=_get_auth(), headers=_get_headers(), stream=stream,
-            params=params)  # type: ignore
+            url, auth=_get_auth(optional=True), headers=_get_headers(),
+            stream=stream, params=params)  # type: ignore
         rsp.raise_for_status()
     except requests.exceptions.RequestException as exc:
         _handle_error('fetch', exc)