Improve AWS region detection by checking AWS_DEFAULT_REGION as fallback (snowflakedb#2535)

Co-authored-by: Patryk Czajka <patryk.czajka@snowflake.com>

Author: mathiasflorin

DESCRIPTION.md

@@ -16,6 +16,7 @@ Source code is also available at: https://github.com/snowflakedb/snowflake-conne
   - Added an option to exclude `botocore` and `boto3` dependencies by setting `SNOWFLAKE_NO_BOTO` environment variable during installation
   - Revert changing exception type in case of token expired scenario for `Oauth` authenticator back to `DatabaseError`
   - Added support for pandas conversion for Day-time and Year-Month Interval types
+  - Fix "No AWS region was found" error if AWS region was set in `AWS_DEFAULT_REGION` variable instead of `AWS_REGION` for `WORKLOAD_IDENTITY` authenticator
   - Add `ocsp_root_certs_dict_lock_timeout` connection parameter to set the timeout (in seconds) for acquiring the lock on the OCSP root certs dictionary. Default value for this parameter is -1 which indicates no timeout.
 
 - v3.17.4(September 22,2025)

src/snowflake/connector/wif_util.py

@@ -96,10 +96,11 @@ def extract_iss_and_sub_without_signature_verification(jwt_str: str) -> tuple[st
 
 def get_aws_region() -> str:
     """Get the current AWS workload's region, or raises an error if it's missing."""
-    region = None
-    if "AWS_REGION" in os.environ:  # Lambda
-        region = os.environ["AWS_REGION"]
-    else:  # EC2
+
+    region = os.environ.get("AWS_REGION") or os.environ.get("AWS_DEFAULT_REGION")
+
+    if not region:
+        # Fallback for EC2 environments
         # TODO: SNOW-2223669 Investigate if our adapters - containing settings of http traffic - should be passed here as boto urllib3session. Those requests go to local servers, so they do not need Proxy setup or Headers customization in theory. But we may want to have all the traffic going through one class (e.g. Adapter or mixin).
         region = InstanceMetadataRegionFetcher().retrieve_region()
 
@@ -108,6 +109,7 @@ def get_aws_region() -> str:
             msg="No AWS region was found. Ensure the application is running on AWS.",
             errno=ER_WIF_CREDENTIALS_NOT_FOUND,
         )
+
     return region