Use os.add_dll_directory when configuring Windows on >=3.8

Author: aiudirog

gssapi/_win_config.py

@@ -7,6 +7,7 @@
 """
 
 import os
+import shutil
 import ctypes
 
 #: Path to normal KfW installed bin folder
@@ -18,8 +19,8 @@
 KFW_DL = "https://web.mit.edu/KERBEROS/dist"
 
 
-def k4w_in_path():
-    """Return if the main GSSAPI DLL for KfW is available in the PATH"""
+def kfw_available():
+    """Return if the main GSSAPI DLL for KfW can be loaded"""
     try:  # to load the main GSSAPI DLL
         ctypes.WinDLL('gssapi64.dll')
     except OSError:  # DLL is not in PATH
@@ -41,14 +42,31 @@ def error_not_found():
 def configure_windows():
     """
     Validate that KfW appears to be installed correctly and add it to the
-    PATH if necessary. In the case that it can't be located, raise an error.
+    DLL directories/PATH if necessary. In the case that it can't be located,
+    raise an error.
     """
-    if k4w_in_path():
+    if kfw_available():
         return  # All set, necessary DLLs should be available
+
     if os.path.exists(KFW_BIN):  # In standard location
-        os.environ['PATH'] += os.pathsep + KFW_BIN
-        if k4w_in_path():
+        try:  # to use Python 3.8's DLL handling
+            os.add_dll_directory(KFW_BIN)
+        except AttributeError:  # <3.8, use PATH
+            os.environ['PATH'] += os.pathsep + KFW_BIN
+        if kfw_available():
             return
+
+    # Check if kinit is in the PATH which should lead us to the bin folder
+    kinit_path = shutil.which('kinit')  # KfW provided binary
+    if kinit_path:  # Non-standard install location
+        try:  # Most likely >=3.8, otherwise it would have been found already
+            os.add_dll_directory(os.path.dirname(kinit_path))
+        except AttributeError:  # <3.8, corrupted installation?
+            pass
+        else:
+            if kfw_available():
+                return
+
     error_not_found()