SNOW-3740779: Keychain support for Linux

What is the current behavior?

The token cache falls back to plaintext file storage on Linux.

What is the desired behavior?

Other similar tools support a D-Bus compliant keychain if available.

How would this improve snowflake-connector-python?

Improve security of credentials storage.

References and other background

POC:

diff --git a/setup.cfg b/setup.cfg
index f612223f..4fb8272c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -111,3 +111,4 @@ pandas =
 secure-local-storage =
     keyring>=23.1.0,<26.0.0
+    jeepney>=0.7;sys_platform=="linux"

diff --git a/src/snowflake/connector/token_cache.py b/src/snowflake/connector/token_cache.py
index 5e71ebb3..43e5978f 100644
--- a/src/snowflake/connector/token_cache.py
+++ b/src/snowflake/connector/token_cache.py
@@ -89,6 +89,14 @@ class TokenCache(ABC):
             return KeyringTokenCache()
 
         if IS_LINUX:
+            # Prefer keyring (D-Bus Secret Service) if a secure backend is available.
+            if installed_keyring:
+                try:
+                    kr = keyring.get_keyring()
+                    if getattr(kr, "priority", 0) > 1:
+                        return KeyringTokenCache()
+                except Exception:
+                    pass
             cache = FileTokenCache.make(skip_file_permissions_check)
             if cache:
                 return cache