Document GH token usage and also make sure we redact them in Process debug output, refs #9757

src/Composer/IO/BaseIO.php

@@ -125,6 +125,8 @@ abstract class BaseIO implements IOInterface, LoggerInterface
         }
 
         foreach ($githubOauth as $domain => $token) {
+            // allowed chars for GH tokens are from https://github.blog/changelog/2021-03-04-authentication-token-format-updates/
+            // plus dots which were at some point used for GH app integration tokens
             if (!preg_match('{^[.A-Za-z0-9_]+$}', $token)) {
                 throw new \UnexpectedValueException('Your github oauth token for '.$domain.' contains invalid characters: "'.$token.'"');
             }

src/Composer/Util/ProcessExecutor.php

@@ -45,7 +45,8 @@ class ProcessExecutor
     {
         if ($this->io && $this->io->isDebug()) {
             $safeCommand = preg_replace_callback('{://(?P<user>[^:/\s]+):(?P<password>[^@\s/]+)@}i', function ($m) {
-                if (preg_match('{^[a-f0-9]{12,}$}', $m['user'])) {
+                // if the username looks like a long (12char+) hex string, or a modern github token (e.g. gp1_xxx) we obfuscate that
+                if (preg_match('{^([a-f0-9]{12,}|g[a-z]\d_[a-zA-Z0-9_]+)$}', $m['user'])) {
                     return '://***:***@';
                 }