test(auth): flaky credentials cache test (#5979)

## Problem
- ran 1000 times in CI, only failed on Windows about 30-40% of the time.
- appears to be a windows `fs` race condition. We delete the credentials
file, then create a new one. If the order of these operations is not
preserved, the test can fail.
- Adding `waitUntil` within the `fs` operations, such that each
operation must succeed before returning, does not fix the problem.
- The credentials file IS updating in time since if we read it right
after generating and before assertion, it is the correct data. This then
implies that the credentials are in fact caching despite the changes to
the credentials file.
- applying `waitUntil` with the condition being that the contents of the
file changed, also did not work since the file content is updating.
- adding certain log statements causes it not to be flaky. 
- While the contents of the file are updating, the stats of the file are
not. This is important, because we use the last modified date to
determine if credentials should refresh in
https://github.com/aws/aws-toolkit-vscode/blob/master/packages/core/src/auth/providers/sharedCredentialsProviderFactory.ts#L37-L45.
- **On windows, it appears the `fs.stat` is unreliable, as we can fully
rewrite the file and its `mtime` and `ctime` fail to update (at least
10+ seconds, potentially never)**
- We can't rely on `fs.stat` on windows machine to determine if
credentials need a refresh. We either need a new mechanism or don't
cache on windows.

## Solution
- Avoid `fs.stat` altogether and refresh by reading the file each time. 
- Added benefit: removes state for tracking modified time, and
simplifies the credentials code.
- Makes a single `fs` call instead of two (two `fs.stat` versus one
`fs.read`).

---

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CONTRIBUTING.md -->

License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: Hweinstock

packages/core/src/auth/providers/sharedCredentialsProviderFactory.ts

@@ -3,47 +3,23 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import fs from '../../shared/fs/fs'
 import { getLogger, Logger } from '../../shared/logger'
 import { loadSharedCredentialsSections, updateAwsSdkLoadConfigEnvVar } from '../credentials/sharedCredentials'
 import { CredentialsProviderType } from './credentials'
 import { BaseCredentialsProviderFactory } from './credentialsProviderFactory'
 import { SharedCredentialsProvider } from './sharedCredentialsProvider'
-import { getCredentialsFilename, getConfigFilename } from '../credentials/sharedCredentialsFile'
 
 export class SharedCredentialsProviderFactory extends BaseCredentialsProviderFactory<SharedCredentialsProvider> {
     private readonly logger: Logger = getLogger()
 
-    private loadedCredentialsModificationMillis?: number
-    private loadedConfigModificationMillis?: number
-
     public async refresh(): Promise<void> {
-        if (await this.needsRefresh()) {
-            await this.loadSharedCredentialsProviders()
-        }
+        await this.loadSharedCredentialsProviders()
     }
 
     public override getProviderType(): CredentialsProviderType | undefined {
         return SharedCredentialsProvider.getProviderType()
     }
 
-    protected override resetProviders() {
-        this.loadedCredentialsModificationMillis = undefined
-        this.loadedConfigModificationMillis = undefined
-
-        super.resetProviders()
-    }
-
-    private async needsRefresh(): Promise<boolean> {
-        const credentialsLastModMillis = await this.getLastModifiedMillis(getCredentialsFilename())
-        const configLastModMillis = await this.getLastModifiedMillis(getConfigFilename())
-
-        return (
-            this.loadedCredentialsModificationMillis !== credentialsLastModMillis ||
-            this.loadedConfigModificationMillis !== configLastModMillis
-        )
-    }
-
     private async loadSharedCredentialsProviders(): Promise<void> {
         this.resetProviders()
 
@@ -52,9 +28,6 @@ export class SharedCredentialsProviderFactory extends BaseCredentialsProviderFac
             const errors = result.errors.map((e) => e.message).join('\t\n')
             getLogger().warn(`credentials: errors while parsing:\n%s`, errors)
         }
-
-        this.loadedCredentialsModificationMillis = await this.getLastModifiedMillis(getCredentialsFilename())
-        this.loadedConfigModificationMillis = await this.getLastModifiedMillis(getConfigFilename())
         await updateAwsSdkLoadConfigEnvVar()
 
         getLogger().verbose(
@@ -79,13 +52,4 @@ export class SharedCredentialsProviderFactory extends BaseCredentialsProviderFac
             this.addProvider(provider)
         }
     }
-
-    private async getLastModifiedMillis(filepath: string): Promise<number | undefined> {
-        try {
-            const stat = await fs.stat(filepath)
-            return stat.mtime
-        } catch (err) {
-            return undefined
-        }
-    }
 }

packages/core/src/test/credentials/provider/sharedCredentialsProviderFactory.test.ts

@@ -120,7 +120,7 @@ describe('SharedCredentialsProviderFactory', async function () {
         )
     })
 
-    it('refresh does not reload from file if the file has not changed', async function () {
+    it('refresh always reloads from file', async function () {
         const sut = new SharedCredentialsProviderFactory()
 
         // First load
@@ -129,10 +129,7 @@ describe('SharedCredentialsProviderFactory', async function () {
         // Expect: No reload
         await sut.refresh()
 
-        assert.ok(
-            loadSharedCredentialsSectionsStub.calledOnce,
-            'Credentials should have only been loaded from disk once'
-        )
+        assert.ok(loadSharedCredentialsSectionsStub.calledTwice, 'Credentials should have loaded from disk twice')
     })
 
     it('refresh reloads from file if the file has changed', async function () {