Cache token when using Azure Identity

simple_ado/auth/ado_azid_auth.py

@@ -1,22 +1,30 @@
 """Azure Identity authentication auth class."""
 
+import time
+
 from azure.identity import DefaultAzureCredential
+from azure.core.credentials import AccessToken
 from simple_ado.auth.ado_auth import ADOAuth
 
 
 class ADOAzIDAuth(ADOAuth):
     """Azure Identity auth."""
 
+    access_token: AccessToken | None
+
+    def __init__(self) -> None:
+        self.access_token = None
+
     def get_authorization_header(self) -> str:
         """Get the header value.
 
         :return: The header value."""
 
         # The get_token parameter specifies the Azure DevOps resource and requests a token with
         # default permissions for API access.
-        return (
-            "Bearer "
-            + DefaultAzureCredential()
-            .get_token("499b84ac-1321-427f-aa17-267ca6975798/.default")
-            .token
-        )
+        if self.access_token is None or self.access_token.expires_on <= time.time() + 60:
+            self.access_token = DefaultAzureCredential().get_token(
+                "499b84ac-1321-427f-aa17-267ca6975798/.default"
+            )
+
+        return "Bearer " + self.access_token.token