apptainer-registry: add page (#21423)

Signed-off-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>

pages/linux/apptainer-registry.md

@@ -0,0 +1,37 @@
+# apptainer registry
+
+> Manage authentication to OCI/Docker registries.
+> See also: `apptainer pull`, `apptainer push`.
+> More information: <https://apptainer.org/docs/user/main/cli/apptainer_registry.html>.
+
+- List all configured registry credentials:
+
+`apptainer registry list`
+
+- Log in to a registry with a username (password will be prompted):
+
+`apptainer registry login {{[-u|--username]}} {{username}} docker://{{registry}}`
+
+- Log in to a custom OCI registry:
+
+`apptainer registry login {{[-u|--username]}} {{username}} oras://{{registry}}`
+
+- Log in with username and password:
+
+`apptainer registry login {{[-u|--username]}} {{username}} {{[-p|--password]}} {{password}} docker://{{registry}}`
+
+- Log in with a password from `stdin`:
+
+`echo "{{password}}" | apptainer registry login {{[-u|--username]}} {{username}} --password-stdin docker://{{registry}}`
+
+- Log in using a custom authentication file:
+
+`apptainer registry login --authfile {{path/to/auth.json}} {{[-u|--username]}} {{username}} docker://{{registry}}`
+
+- Log out from a registry:
+
+`apptainer registry logout docker://{{registry}}`
+
+- Log out using a custom authentication file:
+
+`apptainer registry logout --authfile {{path/to/auth.json}} docker://{{registry}}`