Add instructions for updating security.txt in web-php (#12316)

[ci skip]

docs/release-process.md

@@ -904,6 +904,25 @@ feature development that cannot go into the new version.
    there is only a single section about PHP X.Y.0, instead of individual
    sections for each pre-release.
 
+4. On the announcement day for the initial stable version (or shortly before),
+   update the `Expires` field in the <https://www.php.net/.well-known/security.txt>
+   file. The `Expires` field should be set to the expected date of the next X.Y.0
+   release (following the one currently being prepared), which is usually the
+   fourth Thursday of November in the next year.
+
+   Following the recommendation of [RFC 9116](https://www.rfc-editor.org/rfc/rfc9116),
+   we maintain an `Expires` time of about a year for our security policies. This
+   provides security researchers with confidence they are using our most
+   up-to-date reporting policies.
+
+   The `security.txt` file is located in the [web-php repository](https://github.com/php/web-php)
+   under the `.well-known/` directory. We may make changes to this file at other
+   times, as needed, but we will always advance the `Expires` timestamp on a
+   yearly cadence, coinciding with our X.Y.0 releases.
+
+   Please see the instructions for
+   [making changes to security.txt](security-policies.md#making-changes-to-securitytxt).
+
 
 ## Prime the selection of release managers for the next version
 

docs/security-policies.md

@@ -0,0 +1,90 @@
+# PHP Security Policies and Process
+
+> [!IMPORTANT]
+> This is a meta document discussing PHP security policies and processes. For the actual
+> PHP security policy, see the PHP [Vulnerability Disclosure Policy][] document.
+
+## PHP.net security.txt file
+
+PHP.net includes a [security.txt][] file that complements the
+[Vulnerability Disclosure Policy][], aiding security vulnerability disclosure.
+This file implements the standard defined in [RFC 9116][], and more information
+is available at <https://securitytxt.org>.
+
+RFC 9116 requires an `Expires` field in `security.txt`, and its recommendation
+is for the `Expires` field to be less than a year in the future. This provides
+security researchers with confidence they are using our most up-to-date
+reporting policies. To facilitate yearly updates to the `Expires` field and
+ensure freshness of the information in `security.txt`, the PHP release managers
+[update the `Expires` field as part of the X.Y.0 GA release][expires-update].
+
+From time-to-time, we may update `security.txt` with new information, outside
+of the yearly changes to the `Expires` field.
+
+### Making changes to security.txt
+
+All changes to `security.txt` must be signed by a PHP release manager for a
+[currently supported version of PHP][supported-versions] (at the time of the
+changes). Release managers are the most logical choice for signing this file,
+since we already [publish their PGP keys][rm-pgp-keys].
+
+To make changes to `security.txt`:
+
+1. Go to your local clone of [web-php][].
+
+   ```bash
+   cd /path/to/web-php/.well-known
+   ```
+
+2. Remove the PGP signature that wraps the body of `security.txt`:
+
+   ```bash
+   gpg --decrypt --output security.txt security.txt
+   ```
+
+   > [!NOTE]
+   > To "decrypt" `security.txt`, you will need the public key of the release
+   > manager who last signed it in your GPG keychain.
+
+3. Make and save your changes to this file, e.g., update the `Expires` timestamp.
+
+   There should be a "Signed by" comment in the file that looks similar to this:
+
+   ```
+   # Signed by Ben Ramsey <ramsey@php.net> on 2023-09-28.
+   ```
+
+   Update this line with your name, the email address associated with the key
+   you're using to sign the file, and the current date.
+
+4. Sign your changes:
+
+   ```bash
+   gpg --clearsign --local-user YOU@php.net --output security.txt.asc security.txt
+   ```
+
+   > [!WARNING]
+   > You cannot use `--output` to output the signature to the same file as the
+   > input file or `gpg` will result in a signature wrapped around empty content.
+
+5. Last, replace `security.txt` with `security.txt.asc` and commit your changes:
+
+   ```bash
+   mv security.txt.asc security.txt
+   git commit security.txt
+   ```
+
+> [!NOTE]
+> You may verify the signature with the following command:
+>
+> ```bash
+> gpg --verify security.txt
+> ```
+
+[security.txt]: https://www.php.net/.well-known/security.txt
+[vulnerability disclosure policy]: https://github.com/php/php-src/security/policy
+[rfc 9116]: https://www.rfc-editor.org/rfc/rfc9116
+[expires-update]: release-process.md#preparing-for-the-initial-stable-version-php-xy0
+[supported-versions]: https://www.php.net/supported-versions.php
+[rm-pgp-keys]: https://www.php.net/gpg-keys.php
+[web-php]: https://github.com/php/web-php