s3: enforce authentication and JSON error format for Iceberg REST Catalog (#8192)

* s3: enforce authentication and JSON error format for Iceberg REST Catalog

* s3/iceberg: align error exception types with OpenAPI spec examples

* s3api: refactor AuthenticateRequest to return identity object

* s3/iceberg: propagate full identity object to request context

* s3/iceberg: differentiate NotAuthorizedException and ForbiddenException

* s3/iceberg: reject requests if authenticator is nil to prevent auth bypass

* s3/iceberg: refactor Auth middleware to build context incrementally and use switch for error mapping

* s3api: update misleading comment for authRequestWithAuthType

* s3api: return ErrAccessDenied if IAM is not configured to prevent auth bypass

* s3/iceberg: optimize context update in Auth middleware

* s3api: export CanDo for external authorization use

* s3/iceberg: enforce identity-based authorization in all API handlers

* s3api: fix compilation errors by updating internal CanDo references

* s3/iceberg: robust identity validation and consistent action usage in handlers

* s3api: complete CanDo rename across tests and policy engine integration

* s3api: fix integration tests by allowing admin access when auth is disabled and explicit gRPC ports

* duckdb

* create test bucket

weed/s3api/auth_signature_v2.go

@@ -96,7 +96,7 @@ func (iam *IdentityAccessManagement) doesPolicySignatureV2Match(formValues http.
 	}
 
 	bucket := formValues.Get("bucket")
-	if !identity.canDo(s3_constants.ACTION_WRITE, bucket, "") {
+	if !identity.CanDo(s3_constants.ACTION_WRITE, bucket, "") {
 		return s3err.ErrAccessDenied
 	}