Add HTTP method matching to resource rules

Resolves #1408.

A rule with match "METHOD" carries a comma-separated list of HTTP
methods in its value, e.g. "POST,PUT", and applies when the request
method is in that list. This makes it possible to leave GET public
while sending POST and PUT to auth, which rules could not express
before because both share the same path.

No new columns: the methods live in the existing rule value, so this
needs no migration and every existing rule keeps working unchanged.

The UI offers the ten registered methods. Blueprints and the API
accept any method token, so extension methods such as the WebDAV verbs
can be targeted too, and the UI preserves them when a rule set that
way is edited later.

server/lib/validators.ts

@@ -76,9 +76,46 @@ export const RESOURCE_RULE_MATCH_TYPES = [
     "COUNTRY",
     "COUNTRY_IS_NOT",
     "ASN",
-    "REGION"
+    "REGION",
+    "METHOD"
 ] as const;
 
+// The methods offered in the UI: the eight from RFC 9110 plus PATCH (RFC 5789)
+// and QUERY (RFC 10008). A METHOD rule is not limited to these, since
+// isValidHttpMethodList accepts any method token, so blueprints and the API can
+// also target extension methods such as the WebDAV verbs.
+export const HTTP_METHODS = [
+    "GET",
+    "HEAD",
+    "POST",
+    "PUT",
+    "PATCH",
+    "DELETE",
+    "OPTIONS",
+    "TRACE",
+    "CONNECT",
+    "QUERY"
+] as const;
+
+// RFC 9110 token, minus the characters that would collide with the
+// comma-separated list encoding.
+const HTTP_METHOD_REGEX = /^[!#$%&'*+\-.^_`|~0-9A-Za-z]+$/;
+
+export function parseHttpMethodList(value: string): string[] {
+    return value
+        .split(",")
+        .map((method) => method.trim().toUpperCase())
+        .filter((method) => method.length > 0);
+}
+
+export function isValidHttpMethodList(value: string): boolean {
+    const methods = parseHttpMethodList(value);
+    return (
+        methods.length > 0 &&
+        methods.every((method) => HTTP_METHOD_REGEX.test(method))
+    );
+}
+
 export type ResourceRuleMatchType = (typeof RESOURCE_RULE_MATCH_TYPES)[number];
 
 export function getResourceRuleValueValidationError(
@@ -101,6 +138,10 @@ export function getResourceRuleValueValidationError(
             return COUNTRIES.some((country) => country.code === value)
                 ? null
                 : "Invalid country code provided";
+        case "METHOD":
+            return isValidHttpMethodList(value)
+                ? null
+                : "Invalid HTTP method provided";
         case "ASN":
             const normalizedValue = value.trim().toUpperCase();
             return /^AS\d+$/.test(normalizedValue) ||