docs: Initialize authentication chapter

docs/_meta.json

@@ -14,6 +14,11 @@
         "name": "deploying",
         "label": "Deploying"
     },
+    {
+        "type": "dir",
+        "name": "authentication",
+        "label": "Authentication"
+    },
     {
         "type": "dir",
         "name": "calls",

docs/authentication.mdx

@@ -0,0 +1 @@
+# Authentication

docs/authentication/legacy.mdx

@@ -0,0 +1,14 @@
+# Legacy Authentication
+
+## Registration
+
+Registration is disabled by default. To enable it, set `allow_registration = true` in your config file and follow one of the registration methods below.
+
+### Admin-issued tokens (recommended)
+
+### Static token
+
+### reCAPTCHA
+
+## Email verification
+