Implement request guard to detect enabled sign-up strategy

plume-models/src/signups.rs

@@ -1,3 +1,5 @@
+use crate::CONFIG;
+use rocket::request::{FromRequest, Outcome, Request};
 use std::fmt;
 use std::str::FromStr;
 
@@ -43,3 +45,28 @@ impl fmt::Display for StrategyError {
 }
 
 impl std::error::Error for StrategyError {}
+
+pub struct Password();
+pub struct Email();
+
+impl<'a, 'r> FromRequest<'a, 'r> for Password {
+    type Error = ();
+
+    fn from_request(_request: &'a Request<'r>) -> Outcome<Self, ()> {
+        match matches!(CONFIG.signup, Strategy::Password) {
+            true => Outcome::Success(Self()),
+            false => Outcome::Forward(()),
+        }
+    }
+}
+
+impl<'a, 'r> FromRequest<'a, 'r> for Email {
+    type Error = ();
+
+    fn from_request(_request: &'a Request<'r>) -> Outcome<Self, ()> {
+        match matches!(CONFIG.signup, Strategy::Email) {
+            true => Outcome::Success(Self()),
+            false => Outcome::Forward(()),
+        }
+    }
+}