added support for IAM role authentication

sqlalchemy_media/stores/s3.py

@@ -10,6 +10,7 @@
 # Importing optional stuff required by S3 store
 try:
     from requests_aws4auth import AWS4Auth
+    from botocore.session import Session
 except ImportError:  # pragma: no cover
     AWS4Auth = None
 
@@ -25,6 +26,8 @@
 class S3Store(Store):
     """
     Store for dealing with s3 of aws
+    Refreshable credentials suitable for use with IAM roles
+    can be enabled by leaving access_key and secret_key blank
 
     .. versionadded:: 0.9.0
 
@@ -35,7 +38,7 @@ class S3Store(Store):
     """
     base_url = 'https://{0}.s3.amazonaws.com'
 
-    def __init__(self, bucket: str, access_key: str, secret_key: str,
+    def __init__(self, bucket: str, access_key: str = None, secret_key: str = None,
                  region: str, max_age: int = DEFAULT_MAX_AGE,
                  prefix: str = None, base_url: str = None,
                  cdn_url: str = None, cdn_prefix_ignore: bool = False, 
@@ -65,14 +68,23 @@ def __init__(self, bucket: str, access_key: str, secret_key: str,
 
         self.cdn_url = cdn_url
 
+    def _auth(self):
+        ensure_aws4auth()
+
+        if self.access_key is not None and self.secret_key is not None:
+            return AWS4Auth(self.access_key, self.secret_key, self.region, 's3')
+        else:
+            credentials = Session().get_credentials()
+            return AWS4Auth(region=self.region, service='s3',
+                    refreshable_credentials=credentials)
+
+
     def _get_s3_url(self, filename: str):
         return '{0}/{1}'.format(self.base_url, filename)
 
     def _upload_file(self, url: str, data: str, content_type: str,
                      rrs: bool = False):
-        ensure_aws4auth()
-
-        auth = AWS4Auth(self.access_key, self.secret_key, self.region, 's3')
+        auth = self._auth()
         if rrs:
             storage_class = 'REDUCED_REDUNDANCY'
         else:
@@ -97,17 +109,15 @@ def put(self, filename: str, stream: FileLike):
         return len(data)
 
     def delete(self, filename: str):
-        ensure_aws4auth()
         url = self._get_s3_url(filename)
-        auth = AWS4Auth(self.access_key, self.secret_key, self.region, 's3')
+        auth = self._auth()
         res = requests.delete(url, auth=auth)
         if not 200 <= res.status_code < 300:
             raise S3Error(res.text)
 
     def open(self, filename: str, mode: str = 'rb') -> FileLike:
-        ensure_aws4auth()
         url = self._get_s3_url(filename)
-        auth = AWS4Auth(self.access_key, self.secret_key, self.region, 's3')
+        auth = self._auth()
         res = requests.get(url, auth=auth)
         if not 200 <= res.status_code < 300:
             raise S3Error(res.text)