Set secrets using a middleware

src/cipher/cipher.ml

@@ -11,6 +11,12 @@
 (* TODO LATER Switch to AEAD_AES_256_GCM_SIV. See
    https://github.com/mirage/mirage-crypto/issues/111. *)
 
+
+
+module Dream = Dream_pure
+
+
+
 module type Cipher =
 sig
   val prefix : char
@@ -112,16 +118,46 @@ struct
         | Some plaintext -> Some (Cstruct.to_string plaintext)
 end
 
+let secrets =
+  Dream.new_local
+    ~name:"dream.secret"
+    ~show_value:(fun _secrets -> "[redacted]")
+    ()
+
+(* TODO Add warnings about secret length and such. *)
+(* TODO Also add warnings about implicit secret generation. However, these
+   warnings might be pretty spammy. *)
+(* TODO Update examples and docs. *)
+let with_secret ?(old_secrets = []) secret =
+  let value = secret::old_secrets in
+  fun next_handler request ->
+    request
+    |> Dream.with_local secrets value
+    |> next_handler
+
+let fallback_secrets =
+  lazy [Random.random 32]
+
+let encryption_secret request =
+  match Dream.local secrets request with
+  | Some secrets -> List.hd secrets
+  | None -> List.hd (Lazy.force fallback_secrets)
+
+let decryption_secrets request =
+  match Dream.local secrets request with
+  | Some secrets -> secrets
+  | None -> Lazy.force fallback_secrets
+
 let encrypt ?associated_data request plaintext =
   encrypt
     (module AEAD_AES_256_GCM)
     ?associated_data
-    (Dream_pure.encryption_secret request)
+    (encryption_secret request)
     plaintext
 
 let decrypt ?associated_data request ciphertext =
   decrypt
     (module AEAD_AES_256_GCM)
     ?associated_data
-    (Dream_pure.decryption_secrets request)
+    (decryption_secrets request)
     ciphertext

src/dream.mli

@@ -1973,8 +1973,6 @@ val run :
   ?stop:unit promise ->
   ?debug:bool ->
   ?error_handler:error_handler ->
-  ?secret:string ->
-  ?old_secrets:string list ->
   ?prefix:string ->
   ?https:bool ->
   ?certificate_file:string ->
@@ -2006,18 +2004,6 @@ val run :
       low-level errors. See {!section-errors} and example
       {{:https://github.com/aantron/dream/tree/master/example/9-error#files}
       [9-error]} \[{{:http://dream.as/9-error} playground}\].
-    - [~secret] is a key to be used for cryptographic operations, such as
-      signing CSRF tokens. By default, a random secret is generated on each call
-      to {!Dream.run}. For production, generate a 256-bit key with
-      {[
-        Dream.to_base64url (Dream.random 32)
-      ]}
-      and load it from file. A medium-sized Web app serving 1000 fresh encrypted
-      cookies per second should rotate keys about once a year. See argument
-      [~old_secrets] below for key rotation. See {!Dream.encrypt} for cipher
-      information.
-    - [~old_secrets] is a list of previous secrets that can still be used for
-      decryption, but not for encryption. This is intended for key rotation.
     - [~prefix] is a site prefix for applications that are not running at the
       root ([/]) of their domain. The default is ["/"], for no prefix.
     - [~https:true] enables HTTPS. You should also specify [~certificate_file]
@@ -2050,8 +2036,6 @@ val serve :
   ?stop:unit promise ->
   ?debug:bool ->
   ?error_handler:error_handler ->
-  ?secret:string ->
-  ?old_secrets:string list ->
   ?prefix:string ->
   ?https:bool ->
   ?certificate_file:string ->
@@ -2239,6 +2223,29 @@ val application_json : string
 
 (** {1 Cryptography} *)
 
+val with_secret : ?old_secrets:string list -> string -> middleware
+(** Sets a key to be used for cryptographic operations, such as signing CSRF
+    tokens and encrypting cookies.
+
+    If this middleware is not used, a random secret is generated the first time
+    a secret is needed. The random secret persists for the lifetime of the
+    process. This is useful for quick testing and prototyping, but it means that
+    restarts of the server will not be able to verify tokens or decrypt cookies
+    generated by earlier runs, and multiple servers in a load-balancing
+    arrangement will not accept each others' tokens and cookies.
+
+    For production, generate a 256-bit key with
+
+    {[
+      Dream.to_base64url (Dream.random 32)
+    ]}
+
+    [~old_secrets] is a list of previous secrets that will not be used for
+    encryption or signing, but will still be tried for decryption and
+    verification. This is intended for key rotation. A medium-sized Web app
+    serving 1000 fresh encrypted cookies per second should rotate keys about
+    once a year. *)
+
 val random : int -> string
 (** Generates the requested number of bytes using a
     {{:https://github.com/mirage/mirage-crypto} cryptographically secure random

src/http/http.ml

@@ -751,8 +751,6 @@ let serve_with_maybe_https
     ~stop
     ?debug
     ~error_handler
-    ?(secret = Dream__cipher.Random.random 32)
-    ?(old_secrets = [])
     ~prefix
     ~https
     ?certificate_file ?key_file
@@ -775,16 +773,13 @@ let serve_with_maybe_https
 
     (* This check will at least catch secrets like "foo" when used on a public
        interface. *)
-    if not (is_localhost interface) then
+    (* if not (is_localhost interface) then
       if String.length secret < 32 then begin
         log.warning (fun log -> log "Using a short key on a public interface");
         log.warning (fun log ->
           log "Consider using Dream.to_base64url (Dream.random 32)");
-    end;
-
-    (* TODO The interface needs to allow not messing with the secret if an app
-       is passed. *)
-    Dream.set_secrets (secret::old_secrets) app;
+    end; *)
+    (* TODO Make sure there is a similar check in cipher.ml now.Hpack *)
 
     match https with
     | `No ->
@@ -920,8 +915,6 @@ let serve
     ?(stop = never)
     ?debug
     ?(error_handler = Error_handler.default)
-    ?secret
-    ?old_secrets
     ?(prefix = "")
     ?(https = false)
     ?certificate_file
@@ -936,8 +929,6 @@ let serve
     ~stop
     ?debug
     ~error_handler
-    ?secret
-    ?old_secrets
     ~prefix
     ~https:(if https then `OpenSSL else `No)
     ?certificate_file
@@ -955,8 +946,6 @@ let run
     ?(stop = never)
     ?debug
     ?(error_handler = Error_handler.default)
-    ?secret
-    ?old_secrets
     ?(prefix = "")
     ?(https = false)
     ?certificate_file
@@ -1036,8 +1025,6 @@ let run
         ~stop
         ?debug
         ~error_handler
-        ?secret
-        ?old_secrets
         ~prefix
         ~https:(if https then `OpenSSL else `No)
         ?certificate_file ?key_file

src/pure/dream_pure.mli

@@ -140,11 +140,6 @@ val prefix : request -> string
 val internal_prefix : request -> string list
 val path : request -> string list
 val version : request -> int * int
-val encryption_secret : request -> string
-val decryption_secrets : request -> string list
-(* TODO Get the encryption secrets out of here and into the server only.
-   Also try to move the whole "app" mechanism to the server only. However, how
-   will that interact with in-process testing? *)
 val site_prefix : request -> string list
 (* TODO This will be moved out of dream-pure and become just a server-side
    middleware.. *)
@@ -404,7 +399,6 @@ val app : request -> app
 val debug : app -> bool
 val set_debug : bool -> app -> unit
 val app_error_handler : app -> (error -> response promise)
-val set_secrets : string list -> app -> unit
 val set_https : bool -> app -> unit
 val request_from_http :
   app:app ->

src/pure/inmost.ml

@@ -72,7 +72,6 @@ and server = {
 and app = {
   mutable app_debug : bool;
   mutable https : bool;
-  mutable secrets : string list;
   error_handler : error -> response Lwt.t;
   site_prefix : string list;
 }
@@ -127,13 +126,6 @@ let set_debug value app =
 let app_error_handler app =
   app.error_handler
 
-(* TODO Delete; now using key. *)
-let secret app =
-  List.hd app.secrets
-
-let set_secrets secrets app =
-  app.secrets <- secrets
-
 let set_https https app =
   app.https <- https
 
@@ -143,7 +135,6 @@ let site_prefix request =
 let new_app error_handler site_prefix = {
   app_debug = false;
   https = false;
-  secrets = [];
   error_handler;
   site_prefix;
 }
@@ -595,12 +586,6 @@ let rec pipeline middlewares handler =
 let sort_headers headers =
   List.stable_sort (fun (name, _) (name', _) -> compare name name') headers
 
-let encryption_secret request =
-  List.hd request.specific.app.secrets
-
-let decryption_secrets request =
-  request.specific.app.secrets
-
 (* TODO Remove to server-side code. *)
 let multipart_state request =
   request.specific.upload