Add security policy

Author: jamisonbryant

.github/SECURITY.md

@@ -0,0 +1,29 @@
+# Security Policy
+
+## Supported Versions
+
+We support fixing security issues on the following releases:
+
+| Version | Supported          | Security fixes until
+| ------- | ------------------ | --------------------
+| 4.x     | :white_check_mark: | Currently supported
+| 3.x     | :white_check_mark: | The release of 5.x
+| 2.x     | :white_check_mark: | 36 Months after the release of CakePHP 5.0 (09 Sep 2026)
+| 1.x     | :x:                | No longer supported
+
+## Reporting a Vulnerability
+
+If you've found a security issue in the CakePHP Authentication plugin, please use the following procedure
+instead of the normal bug reporting system. Instead of using the bug tracker,
+or one of the support forums please send an email to security [at] cakephp.org. Emails
+sent to this address go to the CakePHP core team on a private mailing list.
+
+For each report, we try to first confirm the vulnerability. Once confirmed,
+the CakePHP team will take the following actions:
+
+* Acknowledge to the reporter that we've received the issue, and are
+  working on a fix. We ask that the reporter keep the issue confidential until we announce it.
+* Get a fix/patch prepared.
+* Prepare a post describing the vulnerability, and the possible exploits.
+* Release new versions of all affected versions.
+* Prominently feature the problem in the release announcement