diff --git a/.gitignore b/.gitignore
index e686a07..86d6572 100644
--- a/.gitignore
+++ b/.gitignore
@@ -47,3 +47,5 @@ nosetests.xml
 .cache/
 
 .pytest_cache/
+
+tmp
diff --git a/src/pycrunch/__init__.py b/src/pycrunch/__init__.py
index caa897a..a19f24e 100644
--- a/src/pycrunch/__init__.py
+++ b/src/pycrunch/__init__.py
@@ -195,6 +195,8 @@
 
 Session = elements.ElementSession
 
+UnsafeSession = elements.UnsafeElementSession
+
 __all__ = [
     'cubes',
     'elements',
diff --git a/src/pycrunch/elements.py b/src/pycrunch/elements.py
index c4a3053..d35267d 100644
--- a/src/pycrunch/elements.py
+++ b/src/pycrunch/elements.py
@@ -360,3 +360,33 @@ def password(self):
             "`session.password` is being deprecated.", PendingDeprecationWarning
         )
         return self.__password
+
+
+class UnsafeElementSession(ElementSession):
+    """
+    A subclass of ElementSession that disables SSL/TLS verification.
+    This is mean to be used for development purposes only.
+    """
+
+    def __init__(
+        self,
+        email=None,
+        password=None,
+        token=None,
+        site_url=None,
+        progress_tracking=None,
+    ):
+        super(UnsafeElementSession, self).__init__(
+            email,
+            password,
+            token,
+            site_url,
+            progress_tracking,
+        )
+
+        # Skip SSL/TLS verification
+        self.verify = False
+
+        if self.token:
+            # Use Bearer token for authentication
+            self.headers.update({"Authorization": "Bearer {}".format(self.token)})
diff --git a/src/pycrunch/importing.py b/src/pycrunch/importing.py
index 06bf6f5..9f6c0e0 100644
--- a/src/pycrunch/importing.py
+++ b/src/pycrunch/importing.py
@@ -5,7 +5,7 @@
 
 import six
 
-from pycrunch import shoji, csvlib
+from pycrunch import csvlib, shoji
 
 
 class Importer(object):
@@ -53,13 +53,13 @@ def wait_for_batch_status(self, batch, status):
             raise ValueError("The batch did not reach the '%s' state in the "
                              "given time. Please check again later." % status)
 
-    def add_source(self, ds, filename, fp, mimetype):
+    def add_source(self, ds, filename, fp, mimetype, data=None):
         """Create a new Source on the given dataset and return its URL."""
         sources_url = ds.user_url.catalogs['sources']
         # Don't call Catalog.post here (which would force application/json);
         # we want requests.Session to set multipart/form-data with a boundary.
         new_source_url = ds.session.post(
-            sources_url, files={"uploaded_file": (filename, fp, mimetype)}
+            sources_url, files={"uploaded_file": (filename, fp, mimetype)}, data=data
         ).headers["Location"]
 
         if self.strict is not None:
diff --git a/src/pycrunch/version.py b/src/pycrunch/version.py
index 22e3a83..91201fc 100644
--- a/src/pycrunch/version.py
+++ b/src/pycrunch/version.py
@@ -1 +1 @@
-__version__ = '0.5.7'
+__version__ = '0.5.8'