Add config for sign up strategy

plume-models/src/signups.rs

@@ -0,0 +1,45 @@
+use std::fmt;
+use std::str::FromStr;
+
+pub enum Strategy {
+    Password,
+    Email,
+}
+
+impl Default for Strategy {
+    fn default() -> Self {
+        Self::Password
+    }
+}
+
+impl FromStr for Strategy {
+    type Err = StrategyError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        use self::Strategy::*;
+
+        match s {
+            "password" => Ok(Password),
+            "email" => Ok(Email),
+            s => Err(StrategyError::Unsupported(s.to_string())),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum StrategyError {
+    Unsupported(String),
+}
+
+impl fmt::Display for StrategyError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use self::StrategyError::*;
+
+        match self {
+            // FIXME: Calc option strings from enum
+            Unsupported(s) => write!(f, "Unsupported strategy: {}. Choose password or email", s),
+        }
+    }
+}
+
+impl std::error::Error for StrategyError {}