diff --git a/adafruit_jwt.py b/adafruit_jwt.py
index 775e152..d8124d4 100644
--- a/adafruit_jwt.py
+++ b/adafruit_jwt.py
@@ -77,8 +77,8 @@ def validate(jwt):
         # Attempt to decode JOSE header
         try:
             jose_header = STRING_TOOLS.urlsafe_b64decode(jwt.split(".")[0])
-        except UnicodeError:
-            raise UnicodeError("Unable to decode JOSE header.")
+        except UnicodeError as unicode_error:
+            raise UnicodeError("Unable to decode JOSE header.") from unicode_error
         # Check for typ and alg in decoded JOSE header
         if "typ" not in jose_header:
             raise TypeError("JOSE Header does not contain required type key.")
@@ -87,17 +87,19 @@ def validate(jwt):
         # Attempt to decode claim set
         try:
             claims = json.loads(STRING_TOOLS.urlsafe_b64decode(jwt.split(".")[1]))
-        except UnicodeError:
-            raise UnicodeError("Invalid claims encoding.")
+        except UnicodeError as unicode_error:
+            raise UnicodeError("Invalid claims encoding.") from unicode_error
         if not hasattr(claims, "keys"):
             raise TypeError("Provided claims is not a JSON dict. object")
         return (jose_header, claims)
 
     @staticmethod
-    def generate(claims, private_key_data=None, algo=None):
+    def generate(claims, private_key_data=None, algo=None, headers=None):
         """Generates and returns a new JSON Web Token.
         :param dict claims: JWT claims set
         :param str private_key_data: Decoded RSA private key data.
+        :param str algo: algorithm to be used. One of None, RS256, RS384 or RS512.
+        :param dict headers: additional headers for the claim.
         :rtype: str
         """
         # Allow for unencrypted JWTs
@@ -108,6 +110,8 @@ def generate(claims, private_key_data=None, algo=None):
         # Create the JOSE Header
         # https://tools.ietf.org/html/rfc7519#section-5
         jose_header = {"typ": "JWT", "alg": algo}
+        if headers:
+            jose_header.update(headers)
         payload = "{}.{}".format(
             STRING_TOOLS.urlsafe_b64encode(json.dumps(jose_header).encode("utf-8")),
             STRING_TOOLS.urlsafe_b64encode(json.dumps(claims).encode("utf-8")),
@@ -139,8 +143,7 @@ def generate(claims, private_key_data=None, algo=None):
 
 # pylint: disable=invalid-name
 class STRING_TOOLS:
-    """Tools and helpers for URL-safe string encoding.
-    """
+    """Tools and helpers for URL-safe string encoding."""
 
     # Some strings for ctype-style character classification
     whitespace = " \t\n\r\v\f"
@@ -179,8 +182,10 @@ def _bytes_from_decode_data(str_data):
         if isinstance(str_data, str):
             try:
                 return str_data.encode("ascii")
-            except:
-                raise ValueError("string argument should contain only ASCII characters")
+            except BaseException as error:
+                raise ValueError(
+                    "string argument should contain only ASCII characters"
+                ) from error
         elif isinstance(str_data, bit_types):
             return str_data
         else: