Use MockCredential for recorded test playback (Azure#2079)

Fixes Azure#2063

Author: heaths

sdk/core/azure_core_test/src/credential.rs

@@ -0,0 +1,31 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+use azure_core::{
+    credentials::{AccessToken, Secret, TokenCredential},
+    date::OffsetDateTime,
+    error::ErrorKind,
+};
+use std::time::Duration;
+
+/// A mock [`TokenCredential`] useful for testing.
+#[derive(Clone, Debug, Default)]
+pub struct MockCredential;
+
+#[cfg_attr(target_arch = "wasm32", async_trait::async_trait(?Send))]
+#[cfg_attr(not(target_arch = "wasm32"), async_trait::async_trait)]
+impl TokenCredential for MockCredential {
+    async fn get_token(&self, scopes: &[&str]) -> azure_core::Result<AccessToken> {
+        let token: Secret = format!("TEST TOKEN {}", scopes.join(" ")).into();
+        let expires_on = OffsetDateTime::now_utc().saturating_add(
+            Duration::from_secs(60 * 5).try_into().map_err(|err| {
+                azure_core::Error::full(ErrorKind::Other, err, "failed to compute expiration")
+            })?,
+        );
+        Ok(AccessToken { token, expires_on })
+    }
+
+    async fn clear_cache(&self) -> azure_core::Result<()> {
+        Ok(())
+    }
+}

sdk/core/azure_core_test/src/lib.rs

@@ -3,12 +3,14 @@
 
 #![doc = include_str!("../README.md")]
 
+mod credential;
 pub mod proxy;
 pub mod recorded;
 mod recording;
 
 use azure_core::Error;
 pub use azure_core::{error::ErrorKind, test::TestMode};
+pub use credential::*;
 pub use proxy::{matchers::*, sanitizers::*};
 pub use recording::*;
 use std::path::{Path, PathBuf};

sdk/core/azure_core_test/src/recording.rs

@@ -13,7 +13,7 @@ use crate::{
         policy::RecordingPolicy,
         Proxy, RecordingId,
     },
-    Matcher, Sanitizer,
+    Matcher, MockCredential, Sanitizer,
 };
 use azure_core::{
     credentials::TokenCredential,
@@ -73,9 +73,12 @@ impl Recording {
     ///
     /// Panics if the [`TokenCredential`] could not be created.
     pub fn credential(&self) -> Arc<dyn TokenCredential> {
-        match DefaultAzureCredential::new() {
-            Ok(credential) => credential as Arc<dyn TokenCredential>,
-            Err(err) => panic!("{err}"),
+        match self.test_mode {
+            TestMode::Playback => Arc::new(MockCredential) as Arc<dyn TokenCredential>,
+            _ => DefaultAzureCredential::new().map_or_else(
+                |err| panic!("failed to create DefaultAzureCredential: {err}"),
+                |cred| cred as Arc<dyn TokenCredential>,
+            ),
         }
     }