Allow creating JWK from x509 keys directly

jose/Jose.mli

@@ -163,6 +163,16 @@ module Jwk : sig
   (** [to_priv_pem t] takes a JWK and returns a result PEM string or a message
       of what went wrong. *)
 
+  val of_priv_x509 :
+    ?use:use ->
+    X509.Private_key.t ->
+    (priv t, [> `Msg of string | `Not_rsa ]) result
+
+  val of_pub_x509 :
+    ?use:use ->
+    X509.Public_key.t ->
+    (public t, [> `Msg of string | `Not_rsa ]) result
+
   val of_priv_json :
     Yojson.Safe.t ->
     ( priv t,

jose/Jwk.ml

@@ -348,6 +348,23 @@ let to_priv_pem (jwk : priv t) =
       Ok (X509.Private_key.encode_pem (`RSA rsa.key) |> Cstruct.to_string)
   | _ -> Error `Not_rsa
 
+let of_priv_x509 ?use x509 : (priv t, [> `Not_rsa ]) result =
+  match x509 with
+  | `RSA priv_key -> Ok (make_priv_rsa ?use priv_key)
+  | `P256 priv_key -> Ok (make_priv_es256 ?use priv_key)
+  | `P384 priv_key -> Ok (make_priv_es384 ?use priv_key)
+  | `P521 priv_key -> Ok (make_priv_es512 ?use priv_key)
+  | _ -> Error (`Msg "key type not supported")
+
+let of_pub_x509 ?use (x509 : X509.Public_key.t) :
+    (public t, [> `Not_rsa ]) result =
+  match x509 with
+  | `RSA public_key -> Ok (make_pub_rsa ?use public_key)
+  | `P256 public_key -> Ok (make_pub_es256 ?use public_key)
+  | `P384 public_key -> Ok (make_pub_es384 ?use public_key)
+  | `P521 public_key -> Ok (make_pub_es512 ?use public_key)
+  | _ -> Error (`Msg "key type not supported")
+
 let oct_to_json (oct : oct) =
   let values =
     [