diff --git a/src/authenticator.rs b/src/authenticator.rs
index fa68076..36b3277 100644
--- a/src/authenticator.rs
+++ b/src/authenticator.rs
@@ -85,13 +85,13 @@ impl<
         self.inner.lock().unwrap().application_secret()
     }
 
-    fn token<'b, I, T>(
+    fn token<I, T>(
         &mut self,
         scopes: I,
     ) -> Box<dyn Future<Item = Token, Error = RequestError> + Send>
     where
-        T: AsRef<str> + Ord + 'b,
-        I: Iterator<Item = &'b T>,
+        T: Into<String>,
+        I: IntoIterator<Item = T>,
     {
         let (scope_key, scopes) = hash_scopes(scopes);
         let store = self.store.clone();
diff --git a/src/device.rs b/src/device.rs
index 83898b2..67d7048 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -44,15 +44,15 @@ impl<
         C: hyper::client::connect::Connect + Sync + 'static,
     > GetToken for DeviceFlow<FD, C>
 {
-    fn token<'b, I, T>(
+    fn token<I, T>(
         &mut self,
         scopes: I,
     ) -> Box<dyn Future<Item = Token, Error = RequestError> + Send>
     where
-        T: AsRef<str> + Ord + 'b,
-        I: Iterator<Item = &'b T>,
+        T: Into<String>,
+        I: IntoIterator<Item = T>,
     {
-        self.retrieve_device_token(Vec::from_iter(scopes.map(|s| s.as_ref().to_string())))
+        self.retrieve_device_token(Vec::from_iter(scopes.into_iter().map(Into::into)))
     }
     fn api_key(&mut self) -> Option<String> {
         None
@@ -413,7 +413,7 @@ mod tests {
                 .create();
 
             let fut = flow
-                .token(vec!["https://www.googleapis.com/scope/1"].iter())
+                .token(vec!["https://www.googleapis.com/scope/1"])
                 .then(|token| {
                     let token = token.unwrap();
                     assert_eq!("accesstoken", token.access_token);
@@ -445,7 +445,7 @@ mod tests {
                 .create();
 
             let fut = flow
-                .token(vec!["https://www.googleapis.com/scope/1"].iter())
+                .token(vec!["https://www.googleapis.com/scope/1"])
                 .then(|token| {
                     assert!(token.is_err());
                     assert!(format!("{}", token.unwrap_err()).contains("invalid_client_id"));
@@ -476,7 +476,7 @@ mod tests {
                 .create();
 
             let fut = flow
-                .token(vec!["https://www.googleapis.com/scope/1"].iter())
+                .token(vec!["https://www.googleapis.com/scope/1"])
                 .then(|token| {
                     assert!(token.is_err());
                     assert!(format!("{}", token.unwrap_err()).contains("Access denied by user"));
diff --git a/src/installed.rs b/src/installed.rs
index 72b38c5..893fbe6 100644
--- a/src/installed.rs
+++ b/src/installed.rs
@@ -61,15 +61,15 @@ where
 impl<FD: FlowDelegate + 'static + Send + Clone, C: hyper::client::connect::Connect + 'static>
     GetToken for InstalledFlow<FD, C>
 {
-    fn token<'b, I, T>(
+    fn token<I, T>(
         &mut self,
         scopes: I,
     ) -> Box<dyn Future<Item = Token, Error = RequestError> + Send>
     where
-        T: AsRef<str> + Ord + 'b,
-        I: Iterator<Item = &'b T>,
+        T: Into<String>,
+        I: IntoIterator<Item = T>,
     {
-        Box::new(self.obtain_token(scopes.into_iter().map(|s| s.as_ref().to_string()).collect()))
+        Box::new(self.obtain_token(scopes.into_iter().map(Into::into).collect()))
     }
     fn api_key(&mut self) -> Option<String> {
         None
@@ -625,7 +625,7 @@ mod tests {
             .create();
 
             let fut = inf
-                .token(vec!["https://googleapis.com/some/scope"].iter())
+                .token(vec!["https://googleapis.com/some/scope"])
                 .and_then(|tok| {
                     assert_eq!("accesstoken", tok.access_token);
                     assert_eq!("refreshtoken", tok.refresh_token);
@@ -653,7 +653,7 @@ mod tests {
             .create();
 
             let fut = inf
-                .token(vec!["https://googleapis.com/some/scope"].iter())
+                .token(vec!["https://googleapis.com/some/scope"])
                 .and_then(|tok| {
                     assert_eq!("accesstoken", tok.access_token);
                     assert_eq!("refreshtoken", tok.refresh_token);
@@ -675,7 +675,7 @@ mod tests {
                 .create();
 
             let fut = inf
-                .token(vec!["https://googleapis.com/some/scope"].iter())
+                .token(vec!["https://googleapis.com/some/scope"])
                 .then(|tokr| {
                     assert!(tokr.is_err());
                     assert!(format!("{}", tokr.unwrap_err()).contains("invalid_code"));
diff --git a/src/service_account.rs b/src/service_account.rs
index a215a3e..598722a 100644
--- a/src/service_account.rs
+++ b/src/service_account.rs
@@ -315,13 +315,13 @@ impl<C: 'static> GetToken for ServiceAccountAccess<C>
 where
     C: hyper::client::connect::Connect,
 {
-    fn token<'b, I, T>(
+    fn token<I, T>(
         &mut self,
         scopes: I,
     ) -> Box<dyn Future<Item = Token, Error = RequestError> + Send>
     where
-        T: AsRef<str> + Ord + 'b,
-        I: Iterator<Item = &'b T>,
+        T: Into<String>,
+        I: IntoIterator<Item = T>,
     {
         let (hash, scps0) = hash_scopes(scopes);
         let cache = self.cache.clone();
@@ -443,7 +443,7 @@ mod tests {
                 .create();
             let mut acc = ServiceAccountAccess::new(key.clone(), client.clone());
             let fut = acc
-                .token(vec!["https://www.googleapis.com/auth/pubsub"].iter())
+                .token(vec!["https://www.googleapis.com/auth/pubsub"])
                 .and_then(|tok| {
                     assert!(tok.access_token.contains("ya29.c.ElouBywiys0Ly"));
                     assert_eq!(Some(3600), tok.expires_in);
@@ -463,7 +463,7 @@ mod tests {
                 .is_some());
             // Test that token is in cache (otherwise mock will tell us)
             let fut = acc
-                .token(vec!["https://www.googleapis.com/auth/pubsub"].iter())
+                .token(vec!["https://www.googleapis.com/auth/pubsub"])
                 .and_then(|tok| {
                     assert!(tok.access_token.contains("ya29.c.ElouBywiys0Ly"));
                     assert_eq!(Some(3600), tok.expires_in);
@@ -482,7 +482,7 @@ mod tests {
                 .create();
             let mut acc = ServiceAccountAccess::new(key.clone(), client.clone());
             let fut = acc
-                .token(vec!["https://www.googleapis.com/auth/pubsub"].iter())
+                .token(vec!["https://www.googleapis.com/auth/pubsub"])
                 .then(|result| {
                     assert!(result.is_err());
                     Ok(()) as Result<(), ()>
@@ -509,7 +509,7 @@ mod tests {
         let mut acc = ServiceAccountAccess::new(key, client);
         println!(
             "{:?}",
-            acc.token(vec!["https://www.googleapis.com/auth/pubsub"].iter())
+            acc.token(vec!["https://www.googleapis.com/auth/pubsub"])
                 .wait()
         );
     }
diff --git a/src/storage.rs b/src/storage.rs
index af6248a..8c63949 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -35,19 +35,15 @@ pub trait TokenStorage {
 }
 
 /// Calculate a hash value describing the scopes, and return a sorted Vec of the scopes.
-pub fn hash_scopes<'a, I, T>(scopes: I) -> (u64, Vec<String>)
+pub fn hash_scopes<I, T>(scopes: I) -> (u64, Vec<String>)
 where
-    T: AsRef<str> + Ord + 'a,
-    I: IntoIterator<Item = &'a T>,
+    T: Into<String>,
+    I: IntoIterator<Item = T>,
 {
-    let mut sv: Vec<&str> = scopes
-        .into_iter()
-        .map(|s| s.as_ref())
-        .collect::<Vec<&str>>();
+    let mut sv: Vec<String> = scopes.into_iter().map(Into::into).collect();
     sv.sort();
     let mut sh = DefaultHasher::new();
-    &sv.hash(&mut sh);
-    let sv = sv.iter().map(|s| s.to_string()).collect();
+    sv.hash(&mut sh);
     (sh.finish(), sv)
 }
 
diff --git a/src/types.rs b/src/types.rs
index f4d6797..72229b7 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -240,13 +240,13 @@ impl FromStr for Scheme {
 /// The `api_key()` method is an alternative in case there are no scopes or
 /// if no user is involved.
 pub trait GetToken {
-    fn token<'b, I, T>(
+    fn token<I, T>(
         &mut self,
         scopes: I,
     ) -> Box<dyn Future<Item = Token, Error = RequestError> + Send>
     where
-        T: AsRef<str> + Ord + 'b,
-        I: Iterator<Item = &'b T>;
+        T: Into<String>,
+        I: IntoIterator<Item = T>;
 
     fn api_key(&mut self) -> Option<String>;