feat: Add mirror and mirror-token inputs for custom Python distribution sources

Users who need custom CPython builds (internal mirrors, GHES-hosted forks,
special build configurations, compliance builds, air-gapped runners) could not
previously point setup-python at anything other than actions/python-versions.

Adds two new inputs:
- `mirror`: base URL hosting versions-manifest.json and the Python
  distributions it references. Defaults to the existing
  https://raw.githubusercontent.com/actions/python-versions/main.
- `mirror-token`: optional token used to authenticate requests to the mirror.

If `mirror` is a raw.githubusercontent.com/{owner}/{repo}/{branch} URL, the
manifest is fetched via the GitHub REST API (authenticated rate limit applies);
otherwise the action falls back to a direct GET of {mirror}/versions-manifest.json.

Token interaction
-----------------

`token` is never forwarded to arbitrary hosts. Auth resolution is per-URL:

  1. if mirror-token is set, use mirror-token
  2. else if token is set AND the target host is github.com,
     *.github.com, or *.githubusercontent.com, use token
  3. else send no auth

Cases:

  Default (no inputs set)
    mirror = default raw.githubusercontent.com URL, mirror-token empty,
    token = github.token.
    → manifest API call and tarball downloads use `token`.
    Identical to prior behavior.

  Custom raw.githubusercontent.com mirror (e.g. personal fork)
    mirror-token empty, token = github.token.
    → manifest API call and tarball downloads use `token`
      (target hosts are GitHub-owned).

  Custom non-GitHub mirror, no mirror-token
    mirror-token empty, token = github.token.
    → manifest fetched via direct URL (no auth attached),
      tarball downloads use no auth.
    `token` is NOT forwarded to the custom host — this is the
    leak-prevention case.

  Custom non-GitHub mirror with mirror-token
    mirror-token set, token may be set.
    → manifest fetch and tarball downloads use `mirror-token`.

  Custom GitHub mirror with both tokens set
    mirror-token wins. Used for both the manifest API call and
    tarball downloads.

.github/workflows/test-python.yml

@@ -61,6 +61,26 @@ jobs:
       - name: Run simple code
         run: python -c 'import math; print(math.factorial(5))'
 
+  setup-versions-via-mirror-input:
+    name: 'Setup via explicit mirror input: ${{ matrix.os }}'
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: setup-python with explicit mirror
+        uses: ./
+        with:
+          python-version: 3.12
+          mirror: https://raw.githubusercontent.com/actions/python-versions/main
+
+      - name: Run simple code
+        run: python -c 'import sys; print(sys.version)'
+
   setup-versions-from-file:
     name: Setup ${{ matrix.python }} ${{ matrix.os }} version file
     runs-on: ${{ matrix.os }}

__tests__/install-python-mirror.test.ts

@@ -0,0 +1,337 @@
+import {jest, describe, it, expect, beforeEach} from '@jest/globals';
+
+// Inputs are read lazily by install-python.ts, so each test can set them
+// before invoking the function under test.
+const inputs: Record<string, string> = {};
+
+// Mock @actions/http-client
+jest.unstable_mockModule('@actions/http-client', () => ({
+  HttpClient: jest.fn().mockImplementation(() => ({
+    getJson: jest.fn()
+  })),
+  HttpClientError: class HttpClientError extends Error {},
+  HttpCodes: {
+    OK: 200,
+    NotFound: 404,
+    InternalServerError: 500
+  }
+}));
+
+// Mock @actions/cache (needed transitively by utils.ts)
+jest.unstable_mockModule('@actions/cache', () => ({
+  saveCache: jest.fn(),
+  restoreCache: jest.fn(),
+  isFeatureAvailable: jest.fn()
+}));
+
+// Mock @actions/tool-cache
+jest.unstable_mockModule('@actions/tool-cache', () => ({
+  getManifestFromRepo: jest.fn(),
+  downloadTool: jest.fn(),
+  extractTar: jest.fn(),
+  extractZip: jest.fn(),
+  HTTPError: class HTTPError extends Error {}
+}));
+
+// Mock @actions/core (needed by install-python.ts)
+jest.unstable_mockModule('@actions/core', () => ({
+  info: jest.fn(),
+  warning: jest.fn(),
+  debug: jest.fn(),
+  error: jest.fn(),
+  notice: jest.fn(),
+  setFailed: jest.fn(),
+  setOutput: jest.fn(),
+  getInput: jest.fn(),
+  getBooleanInput: jest.fn(),
+  getMultilineInput: jest.fn(),
+  addPath: jest.fn(),
+  exportVariable: jest.fn(),
+  saveState: jest.fn(),
+  getState: jest.fn(),
+  setSecret: jest.fn(),
+  isDebug: jest.fn(() => false),
+  startGroup: jest.fn(),
+  endGroup: jest.fn(),
+  group: jest.fn((_name: string, fn: () => Promise<unknown>) => fn()),
+  toPlatformPath: jest.fn((p: string) => p),
+  toWin32Path: jest.fn((p: string) => p),
+  toPosixPath: jest.fn((p: string) => p)
+}));
+
+// Mock @actions/exec (needed by install-python.ts)
+jest.unstable_mockModule('@actions/exec', () => ({
+  exec: jest.fn(),
+  getExecOutput: jest.fn()
+}));
+
+// Import real utils BEFORE mock registration to get real function references
+const realUtils = await import('../src/utils.js');
+
+// Pin the platform so the download/extract assertions below behave the same
+// on every runner OS.
+jest.unstable_mockModule('../src/utils.js', () => ({
+  ...realUtils,
+  IS_WINDOWS: false,
+  IS_LINUX: false
+}));
+
+// Dynamic imports after mocking
+const core = await import('@actions/core');
+const httpm = await import('@actions/http-client');
+const tc = await import('@actions/tool-cache');
+const {
+  getManifestUrl,
+  getManifestFromRepo,
+  getManifestFromURL,
+  installCpythonFromRelease
+} = await import('../src/install-python.js');
+
+const DEFAULT_MIRROR =
+  'https://raw.githubusercontent.com/actions/python-versions/main';
+
+const mockManifest = [
+  {
+    version: '1.0.0',
+    stable: true,
+    files: [
+      {
+        filename: 'tool-v1.0.0-linux-x64.tar.gz',
+        platform: 'linux',
+        arch: 'x64',
+        download_url: 'https://example.com/tool-v1.0.0-linux-x64.tar.gz'
+      }
+    ]
+  }
+];
+
+function setInputs(values: Record<string, string>) {
+  Object.assign(inputs, values);
+}
+
+beforeEach(() => {
+  jest.resetAllMocks();
+  for (const key of Object.keys(inputs)) {
+    delete inputs[key];
+  }
+  (core.getInput as jest.Mock<any>).mockImplementation(
+    (name: string) => inputs[name] ?? ''
+  );
+});
+
+describe('getManifestUrl', () => {
+  it('defaults to the actions/python-versions manifest', () => {
+    expect(getManifestUrl()).toBe(`${DEFAULT_MIRROR}/versions-manifest.json`);
+  });
+
+  it('appends versions-manifest.json to a custom mirror', () => {
+    setInputs({mirror: 'https://mirror.example/py'});
+    expect(getManifestUrl()).toBe(
+      'https://mirror.example/py/versions-manifest.json'
+    );
+  });
+
+  it('strips trailing slashes from the mirror', () => {
+    setInputs({mirror: 'https://mirror.example/py///'});
+    expect(getManifestUrl()).toBe(
+      'https://mirror.example/py/versions-manifest.json'
+    );
+  });
+
+  it('throws on a mirror that is not a valid URL', () => {
+    setInputs({mirror: 'not a url'});
+    expect(() => getManifestUrl()).toThrow(/Invalid 'mirror' URL/);
+  });
+});
+
+describe('getManifestFromRepo mirror resolution', () => {
+  it('resolves the default mirror to actions/python-versions@main with token', async () => {
+    setInputs({token: 'TKN'});
+    (tc.getManifestFromRepo as jest.Mock<any>).mockResolvedValue(mockManifest);
+
+    await getManifestFromRepo();
+
+    expect(tc.getManifestFromRepo).toHaveBeenCalledWith(
+      'actions',
+      'python-versions',
+      'token TKN',
+      'main'
+    );
+  });
+
+  it('extracts owner/repo/branch from a custom raw.githubusercontent.com mirror', async () => {
+    setInputs({
+      token: 'TKN',
+      mirror: 'https://raw.githubusercontent.com/foo/bar/dev'
+    });
+    (tc.getManifestFromRepo as jest.Mock<any>).mockResolvedValue(mockManifest);
+
+    await getManifestFromRepo();
+
+    expect(tc.getManifestFromRepo).toHaveBeenCalledWith(
+      'foo',
+      'bar',
+      'token TKN',
+      'dev'
+    );
+  });
+
+  it('strips a trailing slash before extracting the branch', async () => {
+    setInputs({
+      token: 'TKN',
+      mirror: 'https://raw.githubusercontent.com/foo/bar/main/'
+    });
+    (tc.getManifestFromRepo as jest.Mock<any>).mockResolvedValue(mockManifest);
+
+    await getManifestFromRepo();
+
+    expect(tc.getManifestFromRepo).toHaveBeenCalledWith(
+      'foo',
+      'bar',
+      'token TKN',
+      'main'
+    );
+  });
+
+  it('throws for a non-GitHub mirror so the caller falls back to the raw URL', () => {
+    setInputs({mirror: 'https://mirror.example/py'});
+    expect(() => getManifestFromRepo()).toThrow(/not a GitHub repo URL/);
+    expect(tc.getManifestFromRepo).not.toHaveBeenCalled();
+  });
+
+  it('prefers mirror-token over token for the GitHub API call', async () => {
+    setInputs({
+      token: 'TKN',
+      'mirror-token': 'MTOK',
+      mirror: 'https://raw.githubusercontent.com/foo/bar/main'
+    });
+    (tc.getManifestFromRepo as jest.Mock<any>).mockResolvedValue(mockManifest);
+
+    await getManifestFromRepo();
+
+    expect(tc.getManifestFromRepo).toHaveBeenCalledWith(
+      'foo',
+      'bar',
+      'token MTOK',
+      'main'
+    );
+  });
+
+  it('sends no auth when neither token nor mirror-token is set', async () => {
+    (tc.getManifestFromRepo as jest.Mock<any>).mockResolvedValue(mockManifest);
+
+    await getManifestFromRepo();
+
+    expect(tc.getManifestFromRepo).toHaveBeenCalledWith(
+      'actions',
+      'python-versions',
+      undefined,
+      'main'
+    );
+  });
+});
+
+describe('getManifestFromURL mirror resolution', () => {
+  it('fetches {mirror}/versions-manifest.json without attaching auth', async () => {
+    setInputs({token: 'TKN', mirror: 'https://mirror.example/py'});
+    const getJson = jest.fn(async () => ({result: mockManifest}));
+    (httpm.HttpClient as jest.Mock<any>).mockImplementation(() => ({getJson}));
+
+    await getManifestFromURL();
+
+    expect(getJson).toHaveBeenCalledWith(
+      'https://mirror.example/py/versions-manifest.json'
+    );
+  });
+});
+
+describe('installCpythonFromRelease auth gating', () => {
+  const makeRelease = (downloadUrl: string) =>
+    ({
+      version: '3.12.0',
+      stable: true,
+      release_url: '',
+      files: [
+        {
+          filename: 'python-3.12.0-linux-x64.tar.gz',
+          platform: 'linux',
+          platform_version: '',
+          arch: 'x64',
+          download_url: downloadUrl
+        }
+      ]
+    }) as any;
+
+  // Returns the auth argument tc.downloadTool was called with.
+  async function downloadAuthFor(downloadUrl: string) {
+    (tc.downloadTool as jest.Mock<any>).mockResolvedValue('/tmp/py.tgz');
+    (tc.extractTar as jest.Mock<any>).mockResolvedValue('/tmp/extracted');
+
+    await installCpythonFromRelease(makeRelease(downloadUrl));
+
+    const call = (tc.downloadTool as jest.Mock<any>).mock.calls[0];
+    expect(call[0]).toBe(downloadUrl);
+    return call[2];
+  }
+
+  it('forwards token to github.com download URLs', async () => {
+    setInputs({token: 'TKN'});
+    await expect(
+      downloadAuthFor(
+        'https://github.com/actions/python-versions/releases/download/3.12.0-x/python-3.12.0-linux-x64.tar.gz'
+      )
+    ).resolves.toBe('token TKN');
+  });
+
+  it('forwards token to api.github.com download URLs', async () => {
+    setInputs({token: 'TKN'});
+    await expect(
+      downloadAuthFor('https://api.github.com/repos/x/y/tarball/main')
+    ).resolves.toBe('token TKN');
+  });
+
+  it('forwards token to *.githubusercontent.com download URLs', async () => {
+    setInputs({token: 'TKN'});
+    await expect(
+      downloadAuthFor('https://objects.githubusercontent.com/x/python.tar.gz')
+    ).resolves.toBe('token TKN');
+  });
+
+  it('does NOT forward token to a non-GitHub download URL', async () => {
+    setInputs({token: 'TKN', mirror: 'https://cdn.example'});
+    await expect(
+      downloadAuthFor('https://cdn.example/py.tar.gz')
+    ).resolves.toBeUndefined();
+  });
+
+  it('does NOT forward token to a lookalike host', async () => {
+    setInputs({token: 'TKN', mirror: 'https://evil-github.com'});
+    await expect(
+      downloadAuthFor('https://evil-github.com/py.tar.gz')
+    ).resolves.toBeUndefined();
+  });
+
+  it('forwards mirror-token to a non-GitHub download URL', async () => {
+    setInputs({
+      token: 'TKN',
+      'mirror-token': 'MTOK',
+      mirror: 'https://cdn.example'
+    });
+    await expect(
+      downloadAuthFor('https://cdn.example/py.tar.gz')
+    ).resolves.toBe('token MTOK');
+  });
+
+  it('prefers mirror-token over token for GitHub download URLs', async () => {
+    setInputs({token: 'TKN', 'mirror-token': 'MTOK'});
+    await expect(
+      downloadAuthFor('https://github.com/o/r/releases/download/v/py.tar.gz')
+    ).resolves.toBe('token MTOK');
+  });
+
+  it('sends no auth when no tokens are configured', async () => {
+    await expect(
+      downloadAuthFor('https://github.com/o/r/releases/download/v/py.tar.gz')
+    ).resolves.toBeUndefined();
+  });
+});

action.yml

@@ -16,8 +16,14 @@ inputs:
     description: "Set this option if you want the action to check for the latest available version that satisfies the version spec."
     default: false
   token:
-    description: "The token used to authenticate when fetching Python distributions from https://github.com/actions/python-versions. When running this action on github.com, the default value is sufficient. When running on GHES, you can pass a personal access token for github.com if you are experiencing rate limiting."
+    description: "The token used to authenticate when fetching Python distributions from https://github.com/actions/python-versions. When running this action on github.com, the default value is sufficient. When running on GHES, you can pass a personal access token for github.com if you are experiencing rate limiting. When 'mirror-token' is set, it takes precedence over this input."
     default: ${{ github.server_url == 'https://github.com' && github.token || '' }}
+  mirror:
+    description: "Base URL for downloading Python distributions. Defaults to https://raw.githubusercontent.com/actions/python-versions/main. See docs/advanced-usage.md for details."
+    default: "https://raw.githubusercontent.com/actions/python-versions/main"
+  mirror-token:
+    description: "Token used to authenticate requests to 'mirror'. Takes precedence over 'token'."
+    required: false
   cache-dependency-path:
     description: "Used to specify the path to dependency files. Supports wildcards or a list of file names for caching multiple dependencies."
   update-environment:

dist/setup/index.js

@@ -98693,12 +98693,56 @@ function _unique(values) {
 
 
 
-const TOKEN = getInput('token');
+const DEFAULT_REPO_OWNER = 'actions';
-const AUTH = !TOKEN ? undefined : `token ${TOKEN}`;
+const DEFAULT_REPO_NAME = 'python-versions';
-const MANIFEST_REPO_OWNER = 'actions';
+const DEFAULT_REPO_BRANCH = 'main';
-const MANIFEST_REPO_NAME = 'python-versions';
+const DEFAULT_MIRROR = `https://raw.githubusercontent.com/${DEFAULT_REPO_OWNER}/${DEFAULT_REPO_NAME}/${DEFAULT_REPO_BRANCH}`;
-const MANIFEST_REPO_BRANCH = 'main';
+// Matches https://raw.githubusercontent.com/{owner}/{repo}/{branch}
-const MANIFEST_URL = `https://raw.githubusercontent.com/${MANIFEST_REPO_OWNER}/${MANIFEST_REPO_NAME}/${MANIFEST_REPO_BRANCH}/versions-manifest.json`;
+const REPO_COORDS_RE = /^https:\/\/raw\.githubusercontent\.com\/([^/]+)\/([^/]+)\/([^/]+)\/?$/;
+function getToken() {
+    return getInput('token');
+}
+function getMirrorToken() {
+    return getInput('mirror-token');
+}
+function getMirror() {
+    const raw = (getInput('mirror') || DEFAULT_MIRROR)
+        .trim()
+        .replace(/\/+$/, '');
+    try {
+        new URL(raw);
+    }
+    catch {
+        throw new Error(`Invalid 'mirror' URL: "${raw}"`);
+    }
+    return raw;
+}
+function getManifestUrl() {
+    return `${getMirror()}/versions-manifest.json`;
+}
+function resolveRepoCoords() {
+    const m = REPO_COORDS_RE.exec(getMirror());
+    return m ? { owner: m[1], repo: m[2], branch: m[3] } : null;
+}
+function authForUrl(url) {
+    const mirrorToken = getMirrorToken();
+    if (mirrorToken)
+        return `token ${mirrorToken}`;
+    let host;
+    try {
+        host = new URL(url).host;
+    }
+    catch {
+        return undefined;
+    }
+    const token = getToken();
+    if (token &&
+        (host === 'github.com' ||
+            host.endsWith('.github.com') ||
+            host.endsWith('.githubusercontent.com')))
+        return `token ${token}`;
+    return undefined;
+}
 function getLinuxOsRelease() {
     try {
         const content = external_fs_namespaceObject.readFileSync('/etc/os-release', 'utf8');
@@ -98846,15 +98890,28 @@ async function getManifest() {
     }
 }
 function install_python_getManifestFromRepo() {
-    core_debug(`Getting manifest from ${MANIFEST_REPO_OWNER}/${MANIFEST_REPO_NAME}@${MANIFEST_REPO_BRANCH}`);
+    const coords = resolveRepoCoords();
-    return getManifestFromRepo(MANIFEST_REPO_OWNER, MANIFEST_REPO_NAME, AUTH, MANIFEST_REPO_BRANCH);
+    if (!coords) {
+        throw new Error(`Mirror "${getMirror()}" is not a GitHub repo URL; falling back to raw URL fetch.`);
+    }
+    core_debug(`Getting manifest from ${coords.owner}/${coords.repo}@${coords.branch}`);
+    // api.github.com is a GitHub-owned URL. Prefer MIRROR_TOKEN (the user provided token), fall back to TOKEN.
+    const token = getToken();
+    const mirrorToken = getMirrorToken();
+    const auth = !mirrorToken
+        ? !token
+            ? undefined
+            : `token ${token}`
+        : `token ${mirrorToken}`;
+    return getManifestFromRepo(coords.owner, coords.repo, auth, coords.branch);
 }
 async function getManifestFromURL() {
     core_debug('Falling back to fetching the manifest using raw URL.');
+    const manifestUrl = getManifestUrl();
     const http = new lib_HttpClient('tool-cache');
-    const response = await http.getJson(MANIFEST_URL);
+    const response = await http.getJson(manifestUrl);
     if (!response.result) {
-        throw new Error(`Unable to get manifest from ${MANIFEST_URL}`);
+        throw new Error(`Unable to get manifest from ${manifestUrl}`);
     }
     return response.result;
 }
@@ -98897,7 +98954,7 @@ async function installCpythonFromRelease(release) {
     let pythonPath = '';
     try {
         const fileName = getDownloadFileName(downloadUrl);
-        pythonPath = await downloadTool(downloadUrl, fileName, AUTH);
+        pythonPath = await downloadTool(downloadUrl, fileName, authForUrl(downloadUrl));
         info('Extract downloaded archive');
         let pythonExtractedFolder;
         if (utils_IS_WINDOWS) {
@@ -99015,7 +99072,7 @@ async function useCpythonVersion(version, architecture, updateEnvironment, check
         if (freethreaded) {
             msg.push(`Free threaded versions are only available for Python 3.13.0 and later.`);
         }
-        msg.push(`The list of all available versions can be found here: ${MANIFEST_URL}`);
+        msg.push(`The list of all available versions can be found here: ${getManifestUrl()}`);
         throw new Error(msg.join(external_os_.EOL));
     }
     const _binDir = binDir(installDir);
@@ -99417,8 +99474,8 @@ function findPyPyInstallDirForWindows(pythonVersion) {
 
 
 
-const install_graalpy_TOKEN = getInput('token');
+const TOKEN = getInput('token');
-const install_graalpy_AUTH = !install_graalpy_TOKEN ? undefined : `token ${install_graalpy_TOKEN}`;
+const AUTH = !TOKEN ? undefined : `token ${TOKEN}`;
 async function installGraalPy(graalpyVersion, architecture, allowPreReleases, releases) {
     let downloadDir;
     releases = releases ?? (await getAvailableGraalPyVersions());
@@ -99441,7 +99498,7 @@ async function installGraalPy(graalpyVersion, architecture, allowPreReleases, re
     const downloadUrl = `${foundAsset.browser_download_url}`;
     info(`Downloading GraalPy from "${downloadUrl}" ...`);
     try {
-        const graalpyPath = await downloadTool(downloadUrl, undefined, install_graalpy_AUTH);
+        const graalpyPath = await downloadTool(downloadUrl, undefined, AUTH);
         info('Extracting downloaded archive...');
         if (utils_IS_WINDOWS) {
             downloadDir = await extractZip(graalpyPath);
@@ -99482,8 +99539,8 @@ async function installGraalPy(graalpyVersion, architecture, allowPreReleases, re
 async function getAvailableGraalPyVersions() {
     const http = new lib_HttpClient('tool-cache');
     const headers = {};
-    if (install_graalpy_AUTH) {
+    if (AUTH) {
-        headers.authorization = install_graalpy_AUTH;
+        headers.authorization = AUTH;
     }
     /*
     Get releases first.

docs/advanced-usage.md

@@ -524,6 +524,41 @@ Such a requirement on side-effect could be because you don't want your composite
 
 >**Note:** Python versions used in this action are generated in the [python-versions](https://github.com/actions/python-versions) repository. For macOS and Ubuntu images, python versions are built from the source code. For Windows, the python-versions repository uses installation executable. For more information please refer to the [python-versions](https://github.com/actions/python-versions) repository.
 
+#### Using a custom mirror
+
+The `mirror` input lets you point `setup-python` at a different location for CPython distributions — a personal fork of `actions/python-versions`, an internal mirror, or any server that hosts a `versions-manifest.json` at its root plus the tarballs referenced by that manifest. Default: `https://raw.githubusercontent.com/actions/python-versions/main`.
+
+The manifest is resolved as follows:
+
+- If `mirror` matches `https://raw.githubusercontent.com/{owner}/{repo}/{branch}`, the manifest is fetched via the GitHub REST API (giving you the 5000/hr authenticated rate limit when a token is present).
+- Otherwise, the action fetches `{mirror}/versions-manifest.json` via a direct HTTP GET.
+
+Authentication:
+
+- `token` is forwarded **only** to `github.com` and hosts under `*.github.com` or `*.githubusercontent.com`. It is never sent to a custom mirror.
+- `mirror-token` takes precedence over `token`: if `mirror-token` is set it is used for every authenticated request (manifest fetch and tarball downloads).
+- If `mirror-token` is empty, `token` is used when the target URL is GitHub-owned.
+- If neither applies, requests are anonymous.
+
+Point at a personal fork of `actions/python-versions` (uses the default `token`, fetched via the GitHub API):
+
+```yaml
+- uses: actions/setup-python@v6
+  with:
+    python-version: '3.12'
+    mirror: https://raw.githubusercontent.com/my-org/python-versions/main
+```
+
+Point at an internal mirror with its own credential:
+
+```yaml
+- uses: actions/setup-python@v6
+  with:
+    python-version: '3.12'
+    mirror: https://python-mirror.internal.example
+    mirror-token: ${{ secrets.PYTHON_MIRROR_TOKEN }}
+```
+
 ### PyPy
 
  `setup-python` is able to configure **PyPy** from two sources:

src/find-python.ts

@@ -137,7 +137,7 @@ export async function useCpythonVersion(
       );
     }
     msg.push(
-      `The list of all available versions can be found here: ${installer.MANIFEST_URL}`
+      `The list of all available versions can be found here: ${installer.getManifestUrl()}`
     );
     throw new Error(msg.join(os.EOL));
   }

src/install-python.ts

@@ -9,12 +9,67 @@ import * as semver from 'semver';
 import {IS_WINDOWS, IS_LINUX, getDownloadFileName} from './utils.js';
 import {IToolRelease} from '@actions/tool-cache';
 
-const TOKEN = core.getInput('token');
+const DEFAULT_REPO_OWNER = 'actions';
-const AUTH = !TOKEN ? undefined : `token ${TOKEN}`;
+const DEFAULT_REPO_NAME = 'python-versions';
-const MANIFEST_REPO_OWNER = 'actions';
+const DEFAULT_REPO_BRANCH = 'main';
-const MANIFEST_REPO_NAME = 'python-versions';
+const DEFAULT_MIRROR = `https://raw.githubusercontent.com/${DEFAULT_REPO_OWNER}/${DEFAULT_REPO_NAME}/${DEFAULT_REPO_BRANCH}`;
-const MANIFEST_REPO_BRANCH = 'main';
+
-export const MANIFEST_URL = `https://raw.githubusercontent.com/${MANIFEST_REPO_OWNER}/${MANIFEST_REPO_NAME}/${MANIFEST_REPO_BRANCH}/versions-manifest.json`;
+// Matches https://raw.githubusercontent.com/{owner}/{repo}/{branch}
+const REPO_COORDS_RE =
+  /^https:\/\/raw\.githubusercontent\.com\/([^/]+)\/([^/]+)\/([^/]+)\/?$/;
+
+function getToken(): string {
+  return core.getInput('token');
+}
+
+function getMirrorToken(): string {
+  return core.getInput('mirror-token');
+}
+
+function getMirror(): string {
+  const raw = (core.getInput('mirror') || DEFAULT_MIRROR)
+    .trim()
+    .replace(/\/+$/, '');
+  try {
+    new URL(raw);
+  } catch {
+    throw new Error(`Invalid 'mirror' URL: "${raw}"`);
+  }
+  return raw;
+}
+
+export function getManifestUrl(): string {
+  return `${getMirror()}/versions-manifest.json`;
+}
+
+function resolveRepoCoords(): {
+  owner: string;
+  repo: string;
+  branch: string;
+} | null {
+  const m = REPO_COORDS_RE.exec(getMirror());
+  return m ? {owner: m[1], repo: m[2], branch: m[3]} : null;
+}
+
+function authForUrl(url: string): string | undefined {
+  const mirrorToken = getMirrorToken();
+  if (mirrorToken) return `token ${mirrorToken}`;
+  let host: string;
+  try {
+    host = new URL(url).host;
+  } catch {
+    return undefined;
+  }
+  const token = getToken();
+  if (
+    token &&
+    (host === 'github.com' ||
+      host.endsWith('.github.com') ||
+      host.endsWith('.githubusercontent.com'))
+  )
+    return `token ${token}`;
+  return undefined;
+}
 
 interface LinuxOsRelease {
   id: string;
@@ -229,24 +284,34 @@ export async function getManifest(): Promise<tc.IToolRelease[]> {
 }
 
 export function getManifestFromRepo(): Promise<tc.IToolRelease[]> {
+  const coords = resolveRepoCoords();
+  if (!coords) {
+    throw new Error(
+      `Mirror "${getMirror()}" is not a GitHub repo URL; falling back to raw URL fetch.`
+    );
+  }
   core.debug(
-    `Getting manifest from ${MANIFEST_REPO_OWNER}/${MANIFEST_REPO_NAME}@${MANIFEST_REPO_BRANCH}`
+    `Getting manifest from ${coords.owner}/${coords.repo}@${coords.branch}`
-  );
-  return tc.getManifestFromRepo(
-    MANIFEST_REPO_OWNER,
-    MANIFEST_REPO_NAME,
-    AUTH,
-    MANIFEST_REPO_BRANCH
   );
+  // api.github.com is a GitHub-owned URL. Prefer MIRROR_TOKEN (the user provided token), fall back to TOKEN.
+  const token = getToken();
+  const mirrorToken = getMirrorToken();
+  const auth = !mirrorToken
+    ? !token
+      ? undefined
+      : `token ${token}`
+    : `token ${mirrorToken}`;
+  return tc.getManifestFromRepo(coords.owner, coords.repo, auth, coords.branch);
 }
 
 export async function getManifestFromURL(): Promise<tc.IToolRelease[]> {
   core.debug('Falling back to fetching the manifest using raw URL.');
 
+  const manifestUrl = getManifestUrl();
   const http: httpm.HttpClient = new httpm.HttpClient('tool-cache');
-  const response = await http.getJson<tc.IToolRelease[]>(MANIFEST_URL);
+  const response = await http.getJson<tc.IToolRelease[]>(manifestUrl);
   if (!response.result) {
-    throw new Error(`Unable to get manifest from ${MANIFEST_URL}`);
+    throw new Error(`Unable to get manifest from ${manifestUrl}`);
   }
   return response.result;
 }
@@ -291,7 +356,11 @@ export async function installCpythonFromRelease(release: tc.IToolRelease) {
   let pythonPath = '';
   try {
     const fileName = getDownloadFileName(downloadUrl);
-    pythonPath = await tc.downloadTool(downloadUrl, fileName, AUTH);
+    pythonPath = await tc.downloadTool(
+      downloadUrl,
+      fileName,
+      authForUrl(downloadUrl)
+    );
     core.info('Extract downloaded archive');
     let pythonExtractedFolder;
     if (IS_WINDOWS) {