JS: add ad hoc whitelist checks as sanitizers

javascript/ql/src/semmle/javascript/dataflow/TaintTracking.qll

@@ -625,6 +625,28 @@ module TaintTracking {
 
   }
 
+  /**
+   * A check of the form `if(<isWhitelisted>(x))`, which sanitizes `x` in its "then" branch.
+   *
+   * `<isWhitelisted>` is a call with callee name 'safe', 'whitelist', 'allow', or similar.
+   */
+  private class AdHocWhitelistCheckSanitizer extends AdditionalSanitizerGuardNode, DataFlow::CallNode {
+    AdHocWhitelistCheckSanitizer() {
+      getCalleeName().regexpMatch("(?i).*(safe|whitelist|allow|auth).*") and
+      getNumArgument() = 1
+    }
+
+    override predicate sanitizes(boolean outcome, Expr e) {
+      outcome = true and
+      e = getArgument(0).asExpr()
+    }
+
+    override predicate appliesTo(Configuration cfg) {
+      any()
+    }
+
+  }
+
   /** A check of the form `if(x in o)`, which sanitizes `x` in its "then" branch. */
   class InSanitizer extends AdditionalSanitizerGuardNode, DataFlow::ValueNode {