fix(cli): region specified in ~/.aws/credentials is ignored (#32133)

We just didn't consider the shared credentials file as returned by the SDK when loading configuration. 

Closes #32130.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/api/aws-auth/awscli-compatible.ts

@@ -149,7 +149,25 @@ export class AwsCliCompatible {
  */
 async function getRegionFromIni(profile: string): Promise<string | undefined> {
   const sharedFiles = await loadSharedConfigFiles({ ignoreCache: true });
-  return sharedFiles?.configFile?.[profile]?.region || sharedFiles?.configFile?.default?.region;
+
+  // Priority:
+  //
+  // credentials come before config because aws-cli v1 behaves like that.
+  //
+  // 1. profile-region-in-credentials
+  // 2. profile-region-in-config
+  // 3. default-region-in-credentials
+  // 4. default-region-in-config
+
+  return getRegionFromIniFile(profile, sharedFiles.credentialsFile)
+    ?? getRegionFromIniFile(profile, sharedFiles.configFile)
+    ?? getRegionFromIniFile('default', sharedFiles.credentialsFile)
+    ?? getRegionFromIniFile('default', sharedFiles.configFile);
+
+}
+
+function getRegionFromIniFile(profile: string, data?: any) {
+  return data?.[profile]?.region;
 }
 
 function tryGetCACert(bundlePath?: string) {

packages/aws-cdk/test/api/aws-auth/awscli-compatible.test.ts

@@ -1,5 +1,291 @@
+import * as os from 'os';
+import * as path from 'path';
+import * as fs from 'fs-extra';
 import { AwsCliCompatible } from '../../../lib/api/aws-auth/awscli-compatible';
 
+describe('AwsCliCompatible.region', () => {
+
+  beforeEach(() => {
+
+    // make sure we don't mistakenly point to an unrelated file
+    process.env.AWS_CONFIG_FILE = '/dev/null';
+    process.env.AWS_SHARED_CREDENTIALS_FILE = '/dev/null';
+
+    // these take precedence over the ini files so we need to disable them for
+    // the test to invoke the right function
+    delete process.env.AWS_REGION;
+    delete process.env.AMAZON_REGION;
+    delete process.env.AWS_DEFAULT_REGION;
+    delete process.env.AMAZON_DEFAULT_REGION;
+
+  });
+
+  test('default region can be specified in config', async () => {
+
+    const config = `
+  [default]
+  region=region-in-config
+  `;
+
+    await expect(region({ configFile: config })).resolves.toBe('region-in-config');
+  });
+
+  test('default region can be specified in credentials', async () => {
+
+    const creds = `
+  [default]
+  region=region-in-credentials
+  `;
+
+    await expect(region({ credentialsFile: creds })).resolves.toBe('region-in-credentials');
+
+  });
+
+  test('profile region can be specified in config', async () => {
+
+    const config = `
+  [profile user1]
+  region=region-in-config
+  `;
+
+    await expect(region({ configFile: config, profile: 'user1' })).resolves.toBe('region-in-config');
+
+  });
+
+  test('profile region can be specified in credentials', async () => {
+
+    const creds = `
+  [user1]
+  region=region-in-credentials
+  `;
+
+    await expect(region({ credentialsFile: creds, profile: 'user1' })).resolves.toBe('region-in-credentials');
+
+  });
+
+  test('with profile | profile-region-in-credentials is priority 1', async () => {
+
+    const config = `
+  [default]
+  region=default-region-in-config
+
+  [profile user]
+  region=profile-region-in-config
+
+  `;
+
+    const creds = `
+  [default]
+  region=default-region-in-credentials
+
+  [user]
+  region=profile-region-in-credentials
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config, profile: 'user' })).resolves.toBe('profile-region-in-credentials');
+  });
+
+  test('with profile | profile-region-in-config is priority 2', async () => {
+
+    const config = `
+  [default]
+  region=default-region-in-config
+
+  [profile user]
+  region=profile-region-in-config
+
+  `;
+
+    const creds = `
+  [default]
+  region=default-region-in-credentials
+
+  [user]
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config, profile: 'user' })).resolves.toBe('profile-region-in-config');
+  });
+
+  test('with profile | default-region-in-credentials is priority 3', async () => {
+
+    const config = `
+  [default]
+  region=default-region-in-config
+
+  [profile user]
+
+  `;
+
+    const creds = `
+  [default]
+  region=default-region-in-credentials
+
+  [user]
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config, profile: 'user' })).resolves.toBe('default-region-in-credentials');
+  });
+
+  test('with profile | default-region-in-config is priority 4', async () => {
+
+    const config = `
+  [default]
+  region=default-region-in-config
+
+  [profile user]
+
+  `;
+
+    const creds = `
+  [default]
+
+  [user]
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config, profile: 'user' })).resolves.toBe('default-region-in-config');
+  });
+
+  test('with profile | us-east-1 is priority 5', async () => {
+
+    const config = `
+  [default]
+
+  [profile user]
+
+  `;
+
+    const creds = `
+  [default]
+
+  [user]
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config, profile: 'user' })).resolves.toBe('us-east-1');
+  });
+
+  test('without profile | default-region-in-credentials is priority 1', async () => {
+
+    const config = `
+  [default]
+  region=default-region-in-config
+
+  `;
+
+    const creds = `
+  [default]
+  region=default-region-in-credentials
+
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config })).resolves.toBe('default-region-in-credentials');
+  });
+
+  test('without profile | default-region-in-config is priority 2', async () => {
+
+    const config = `
+  [default]
+  region=default-region-in-config
+
+  `;
+
+    const creds = `
+  [default]
+
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config })).resolves.toBe('default-region-in-config');
+  });
+
+  test('without profile | us-east-1 is priority 3', async () => {
+
+    const config = `
+  [default]
+
+  `;
+
+    const creds = `
+  [default]
+
+  `;
+
+    await expect(region({ credentialsFile: creds, configFile: config })).resolves.toBe('us-east-1');
+  });
+
+});
+
+async function region(opts: {
+  readonly configFile?: string;
+  readonly credentialsFile?: string;
+  readonly profile?: string;
+}) {
+
+  const workdir = fs.mkdtempSync(path.join(os.tmpdir(), 'awscli-compatible.test'));
+
+  try {
+
+    if (opts.configFile) {
+      const configPath = path.join(workdir, 'config');
+      fs.writeFileSync(configPath, opts.configFile);
+      process.env.AWS_CONFIG_FILE = configPath;
+    }
+
+    if (opts.credentialsFile) {
+      const credentialsPath = path.join(workdir, 'credentials');
+      fs.writeFileSync(credentialsPath, opts.credentialsFile);
+      process.env.AWS_SHARED_CREDENTIALS_FILE = credentialsPath;
+    }
+
+    return await AwsCliCompatible.region(opts.profile);
+
+  } finally {
+    fs.removeSync(workdir);
+  }
+}
+
+describe('Session token', () => {
+  beforeEach(() => {
+    process.env.AWS_ACCESS_KEY_ID = 'foo';
+    process.env.AWS_SECRET_ACCESS_KEY = 'bar';
+  });
+
+  test('does not mess up with session token env variables if they are undefined', async () => {
+    // Making sure these variables are not defined
+    delete process.env.AWS_SESSION_TOKEN;
+    delete process.env.AMAZON_SESSION_TOKEN;
+
+    await AwsCliCompatible.credentialChainBuilder();
+
+    expect(process.env.AWS_SESSION_TOKEN).toBeUndefined();
+  });
+
+  test('preserves AWS_SESSION_TOKEN if it is defined', async () => {
+    process.env.AWS_SESSION_TOKEN = 'aaa';
+    delete process.env.AMAZON_SESSION_TOKEN;
+
+    await AwsCliCompatible.credentialChainBuilder();
+
+    expect(process.env.AWS_SESSION_TOKEN).toEqual('aaa');
+  });
+
+  test('assigns AWS_SESSION_TOKEN if it is not defined but AMAZON_SESSION_TOKEN is', async () => {
+    delete process.env.AWS_SESSION_TOKEN;
+    process.env.AMAZON_SESSION_TOKEN = 'aaa';
+
+    await AwsCliCompatible.credentialChainBuilder();
+
+    expect(process.env.AWS_SESSION_TOKEN).toEqual('aaa');
+  });
+
+  test('preserves AWS_SESSION_TOKEN if both are defined', async () => {
+    process.env.AWS_SESSION_TOKEN = 'aaa';
+    process.env.AMAZON_SESSION_TOKEN = 'bbb';
+
+    await AwsCliCompatible.credentialChainBuilder();
+
+    expect(process.env.AWS_SESSION_TOKEN).toEqual('aaa');
+  });
+});
+
 describe('Session token', () => {
   beforeEach(() => {
     process.env.AWS_ACCESS_KEY_ID = 'foo';