config.ml

open Core

let src = Logs.Src.create "tls.config" ~doc:"TLS config"
module Log = (val Logs.src_log src : Logs.LOG)

type certchain = X509.Certificate.t list * X509.Private_key.t

type own_cert = [
  | `None
  | `Single of certchain
  | `Multiple of certchain list
  | `Multiple_default of certchain * certchain list
]

let pp_cert ppf cs =
  let from, until = X509.Certificate.validity cs in
  Fmt.pf ppf "subject %a@ issuer %a@ valid from %a until %a"
    X509.Distinguished_name.pp (X509.Certificate.subject cs)
    X509.Distinguished_name.pp (X509.Certificate.issuer cs)
    (Ptime.pp_human ~tz_offset_s:0 ()) from
    (Ptime.pp_human ~tz_offset_s:0 ()) until

let pp_certchain ppf (chain, _) =
  Fmt.(list ~sep:(any "@.") pp_cert) ppf chain

let pp_own_cert ppf = function
  | `None -> Fmt.string ppf "NONE"
  | `Single chain -> pp_certchain ppf chain
  | `Multiple cs ->
    Fmt.pf ppf "multiple: %a" Fmt.(list ~sep:(any "@.@.") pp_certchain) cs
  | `Multiple_default (c, cs) ->
    Fmt.pf ppf "multiple default:@.%a@.others:@.%a"
      pp_certchain c
      Fmt.(list ~sep:(any "@.@.") pp_certchain) cs

type session_cache = SessionID.t -> epoch_data option

type ticket_cache = {
  lookup : string -> (psk13 * epoch_data) option ;
  ticket_granted : psk13 -> epoch_data -> unit ;
  lifetime : int32 ;
  timestamp : unit -> Ptime.t
}

(* TODO: min_rsa, min_dh *)
type config = {
  ciphers : Ciphersuite.ciphersuite list ;
  protocol_versions : tls_version * tls_version ;
  signature_algorithms : signature_algorithm list ;
  use_reneg : bool ;
  authenticator : X509.Authenticator.t option ;
  peer_name : [`host] Domain_name.t option ;
  own_certificates : own_cert ;
  acceptable_cas : X509.Distinguished_name.t list ;
  session_cache : session_cache ;
  ticket_cache : ticket_cache option ;
  cached_session : epoch_data option ;
  cached_ticket : (psk13 * epoch_data) option ;
  alpn_protocols : string list ;
  groups : group list ;
  zero_rtt : int32 ;
  ip : Ipaddr.t option ;
}

let pp_config ppf cfg =
  Fmt.pf ppf
    "ciphers: %a@. \
     minimal protocol version: %a@. \
     maximum protocol version: %a@. \
     signature algorithms: %a@. \
     renegotiation enabled %B@. \
     peer name: %a@. \
     own certificate: %a@. \
     acceptable CAs: %a@. \
     alpn protocols: %a@. \
     groups: %a@. \
     IP: %a@."
    Fmt.(list ~sep:(any ", ") Ciphersuite.pp_ciphersuite) cfg.ciphers
    pp_tls_version (fst cfg.protocol_versions)
    pp_tls_version (snd cfg.protocol_versions)
    Fmt.(list ~sep:(any ", ") pp_signature_algorithm) cfg.signature_algorithms
    cfg.use_reneg
    Fmt.(option ~none:(any "none provided") Domain_name.pp) cfg.peer_name
    pp_own_cert cfg.own_certificates
    Fmt.(list ~sep:(any ", ") X509.Distinguished_name.pp) cfg.acceptable_cas
    Fmt.(list ~sep:(any ", ") string) cfg.alpn_protocols
    Fmt.(list ~sep:(any ", ") pp_group) cfg.groups
    Fmt.(option ~none:(any "none provided") Ipaddr.pp) cfg.ip

let ciphers13 cfg =
  List.rev
    (List.fold_left (fun acc cs ->
         match Ciphersuite.ciphersuite_to_ciphersuite13 cs with
         | None -> acc
         | Some c -> c :: acc)
        [] cfg.ciphers)

module Ciphers = struct

  (* A good place for various pre-baked cipher lists and helper functions to
   * slice and groom those lists. *)

  let default13 = [
    `AES_128_GCM_SHA256 ;
    `AES_256_GCM_SHA384 ;
    `CHACHA20_POLY1305_SHA256 ;
    `AES_128_CCM_SHA256 ;
  ]

  let default = default13 @ [
    `DHE_RSA_WITH_AES_256_GCM_SHA384 ;
    `DHE_RSA_WITH_AES_128_GCM_SHA256 ;
    `DHE_RSA_WITH_AES_256_CCM ;
    `DHE_RSA_WITH_AES_128_CCM ;
    `DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 ;
    `ECDHE_RSA_WITH_AES_128_GCM_SHA256 ;
    `ECDHE_RSA_WITH_AES_256_GCM_SHA384 ;
    `ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 ;
    `ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 ;
    `ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 ;
    `ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 ;
    ]

  let supported = default @ [
      `DHE_RSA_WITH_AES_256_CBC_SHA256 ;
      `DHE_RSA_WITH_AES_128_CBC_SHA256 ;
      `DHE_RSA_WITH_AES_256_CBC_SHA ;
      `DHE_RSA_WITH_AES_128_CBC_SHA ;
      `ECDHE_RSA_WITH_AES_256_CBC_SHA384 ;
      `ECDHE_RSA_WITH_AES_128_CBC_SHA256 ;
      `ECDHE_RSA_WITH_AES_256_CBC_SHA ;
      `ECDHE_RSA_WITH_AES_128_CBC_SHA ;
      `ECDHE_ECDSA_WITH_AES_128_CBC_SHA ;
      `ECDHE_ECDSA_WITH_AES_256_CBC_SHA ;
      `ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 ;
      `ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 ;
      `RSA_WITH_AES_256_CBC_SHA256 ;
      `RSA_WITH_AES_128_CBC_SHA256 ;
      `RSA_WITH_AES_256_CBC_SHA ;
      `RSA_WITH_AES_128_CBC_SHA ;
      `RSA_WITH_AES_256_GCM_SHA384 ;
      `RSA_WITH_AES_128_GCM_SHA256 ;
      `RSA_WITH_AES_256_CCM ;
      `RSA_WITH_AES_128_CCM ;
      `DHE_RSA_WITH_3DES_EDE_CBC_SHA ;
      `RSA_WITH_3DES_EDE_CBC_SHA ;
      `ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA ;
    ]

  (* as defined in https://httpwg.org/specs/rfc7540.html#BadCipherSuites *)
  let http2 = default13 @ [
    `DHE_RSA_WITH_AES_256_GCM_SHA384 ;
    `DHE_RSA_WITH_AES_128_GCM_SHA256 ;
    `DHE_RSA_WITH_AES_256_CCM ;
    `DHE_RSA_WITH_AES_128_CCM ;
    `DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 ;
    `ECDHE_RSA_WITH_AES_128_GCM_SHA256 ;
    `ECDHE_RSA_WITH_AES_256_GCM_SHA384 ;
    `ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 ;
    `ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 ;
    `ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 ;
    `ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 ;
  ]

  let fs_of = List.filter Ciphersuite.ciphersuite_fs

  let fs = fs_of default
end

let default_signature_algorithms =
  [ `ECDSA_SECP256R1_SHA256 ;
    `ECDSA_SECP384R1_SHA384 ;
    `ECDSA_SECP521R1_SHA512 ;
    `ED25519 ;
    `RSA_PSS_RSAENC_SHA256 ;
    `RSA_PSS_RSAENC_SHA384 ;
    `RSA_PSS_RSAENC_SHA512 ;
    `RSA_PKCS1_SHA256 ;
    `RSA_PKCS1_SHA384 ;
    `RSA_PKCS1_SHA512 ;
  ]

let supported_signature_algorithms =
  default_signature_algorithms @ [
    `RSA_PKCS1_SHA224 ;
    `ECDSA_SECP256R1_SHA1 ;
    `RSA_PKCS1_SHA1 ;
    `RSA_PKCS1_MD5
  ]

let min_dh_size = 1024

let min_rsa_key_size = 1024

let supported_groups =
  [ `X25519 ; `P384 ; `P256 ; `P521 ;
    `FFDHE2048 ; `FFDHE3072 ; `FFDHE4096 ; `FFDHE6144 ; `FFDHE8192 ]

let elliptic_curve = function
  | `X25519 | `P256 | `P384 | `P521 -> true
  | `FFDHE2048 | `FFDHE3072 | `FFDHE4096 | `FFDHE6144 | `FFDHE8192 -> false

let default_config = {
  ciphers = Ciphers.default ;
  protocol_versions = (`TLS_1_2, `TLS_1_3) ;
  signature_algorithms = default_signature_algorithms ;
  use_reneg = false ;
  authenticator = None ;
  peer_name = None ;
  own_certificates = `None ;
  acceptable_cas = [] ;
  session_cache = (fun _ -> None) ;
  cached_session = None ;
  cached_ticket = None ;
  alpn_protocols = [] ;
  groups = supported_groups ;
  ticket_cache = None ;
  zero_rtt = 0l ;
  ip = None ;
}

(* There are inter-configuration option constraints that are checked and
   adjusted here. The overall approach is if the client explicitly provided
   values, these are taken as granted (a conflict will result in an error). If
   the defaults are used, they are adjusted depending on the others.

   The options in question are:
   - ciphers, which before 1.3 include the key exchange (FFDHE, ECDHE, RSA)
   - groups, which name the FFDHE and ECDHE groups used for DH
   - signature_algorithms, which (since 1.2) specify the key type and algorithm
     used for signatures (RSA-PKCS, RSA-PSS, ECDSA/EdDSA)
   - certificate chains, which influence ciphers (before 1.3) and
     signature_algorithms

   Using everywhere the default (but a custom certificate / or multiple) result
   in a working configuration (where, depending on the certificate key type,
   some signature_algorithms and ciphersuites are removed). The provided server
   certificate may remove ciphers & signature_algorithms, but will only result
   in failure if these will then be empty.

   An invalid configuration is for example: only FFDHE ciphersuites, but no
   FFDHE groups. Or only EC signature algorithms, but only ciphers where the
   key type is RSA.

   At session initiation time, the server implementation selects cipher,
   certificate, signature_algorithm, and group depending on its configuration
   and client request.
*)

let ciphers_and_groups ?ciphers ?groups default_ciphers =
  let tls13 = function #Ciphersuite.ciphersuite13 -> true | _ -> false in
  match ciphers, groups with
  | None, None -> Ok (default_ciphers, supported_groups)
  | Some cs, None ->
    Ok (cs,
        let has_kex x = function
          | #Ciphersuite.ciphersuite13 -> true
          | c -> x = Ciphersuite.ciphersuite_kex c
        in
        begin
          match List.exists (has_kex `ECDHE) cs, List.exists (has_kex `FFDHE) cs with
          | true, true -> supported_groups
          | true, false ->
            Log.warn (fun m -> m "removed FFDHE groups (no FFDHE ciphersuite) from configuation");
            List.filter elliptic_curve supported_groups
          | false, true ->
            Log.warn (fun m -> m "removed ECDHE groups (no ECDHE ciphersuite) from configuration");
            List.filter (fun g -> not (elliptic_curve g)) supported_groups
          | false, false -> []
        end)
  | None, Some g ->
    Ok (begin match List.partition elliptic_curve g with
        | [], [] ->
          Log.warn (fun m -> m "removed DHE and ECDHE ciphersuites (empty groups provided) from configuration");
          List.filter (fun c -> not (Ciphersuite.ciphersuite_fs c)) default_ciphers
        | _::_, [] ->
          Log.warn (fun m -> m "removed DHE ciphersuites (no FFDHE groups provided) from configuration");
          List.filter (fun c -> not (Ciphersuite.dhe_only c)) default_ciphers
        | [], _ :: _ ->
          Log.warn (fun m -> m "removed ECDHE ciphersuites (no EC groups provided) from configuration");
          List.filter (fun c -> not (Ciphersuite.ecdhe_only c)) default_ciphers
        | _ -> default_ciphers
      end, g)
  | Some cs, Some g ->
    if List.exists Ciphersuite.ecdhe_only cs && not (List.exists elliptic_curve g) then
      Error (`Msg "ciphersuite with ECDHE provided, but no EC group")
    else if List.exists Ciphersuite.dhe_only cs && not (List.exists (fun g -> not (elliptic_curve g)) g) then
      Error (`Msg "ciphersuite with FFDHE provided, but no FF group")
    else if List.exists Ciphersuite.ciphersuite_fs cs && g = [] then
      Error (`Msg "ciphersuite with forward security provided, but no group")
    else if List.exists elliptic_curve g && not (List.exists Ciphersuite.ecdhe cs) then
      Error (`Msg "EC group provided, but no ciphersuite with ECDHE")
    else if List.exists (fun g -> not (elliptic_curve g)) g &&
       not (List.exists (fun c -> Ciphersuite.dhe_only c || tls13 c) cs)
    then
      Error (`Msg "FF group provided, but no ciphersuite with DHE")
    else
      Ok (cs, g)

let ciphers_and_sig_alg ?ciphers ?signature_algorithms default_ciphers =
  let tls13 = function #Ciphersuite.ciphersuite13 -> true | _ -> false in
  let default_sa_from_ciphers c =
    let has_key k c = tls13 c || k = Ciphersuite.ciphersuite_keytype c in
    match List.exists (has_key `RSA) c, List.exists (has_key `EC) c with
    | true, true -> Ok supported_signature_algorithms
    | true, false ->
      Log.warn (fun m -> m "removed EC signature algorithms (no EC ciphersuite present)");
      Ok (List.filter rsa_sigalg supported_signature_algorithms)
    | false, true ->
      Log.warn (fun m -> m "removed RSA signature algorithms (no RSA ciphersuite present)");
      Ok (List.filter (fun sa -> not (rsa_sigalg sa)) supported_signature_algorithms)
    | false, false ->
      Error (`Msg "ciphersuite list without RSA and EC keys")
  in
  let ( let* ) = Result.bind in
  match ciphers, signature_algorithms with
  | None, None ->
    let* sig_algs = default_sa_from_ciphers default_ciphers in
    Ok (default_ciphers, sig_algs)
  | Some c, None ->
    let* sig_algs = default_sa_from_ciphers c in
    Ok (c, sig_algs)
  | None, Some sa ->
    begin match List.partition rsa_sigalg sa with
      | [], [] -> Error (`Msg "empty signature algorithms provided")
      | _::_, [] ->
        Log.warn (fun m -> m "removing EC ciphers (no EC signature algorithm provided)");
        Ok (List.filter
              (fun c -> tls13 c || not (Ciphersuite.ciphersuite_keytype c = `EC))
              default_ciphers,
            sa)
      | [], _::_ ->
        Log.warn (fun m -> m "removing RSA ciphers (no RSA signature algorithm provided)");
        Ok (List.filter
              (fun c -> tls13 c || not (Ciphersuite.ciphersuite_keytype c = `RSA))
              default_ciphers,
            sa)
      | _::_, _::_ -> Ok (default_ciphers, sa)
    end
  | Some c, Some sa ->
    if List.exists rsa_sigalg sa && not (List.exists (fun c -> Ciphersuite.ciphersuite_keytype c = `RSA) c) then
      Error (`Msg "RSA signature algorithm, but no ciphersuites with RSA keys")
    else if List.exists (fun s -> not (rsa_sigalg s)) sa && not (List.exists (fun c -> Ciphersuite.ciphersuite_keytype c = `EC) c) then
      Error (`Msg "EC signature algorithm, but no ciphersuites with EC keys")
    else if List.exists (fun c -> Ciphersuite.ciphersuite_keytype c = `RSA) c && not (List.exists rsa_sigalg sa) then
      Error (`Msg "RSA ciphersuite, but no RSA signature algorithm")
    else if List.exists (fun c -> Ciphersuite.ciphersuite_keytype c = `EC) c && not (List.exists (fun s -> not (rsa_sigalg s)) sa) then
      Error (`Msg "EC ciphersuite, but no EC signature algorithm")
    else
      Ok (c, sa)

let validate_common config =
  let ( let* ) = Result.bind in
  let (v_min, v_max) = config.protocol_versions in
  if v_max < v_min then
    Error (`Msg "bad version range")
  else
    let* ciphers, signature_algorithms =
      match v_min, v_max with
      | _, `TLS_1_1 | _, `TLS_1_0 ->
        Log.warn (fun m -> m "TLS 1.0 or TLS 1.1 as maximum version configured, removing 1.2 and 1.3 ciphersuites");
        Ok (List.filter (fun c ->
            not (Ciphersuite.ciphersuite_tls12_only c || Ciphersuite.ciphersuite_tls13 c))
            config.ciphers,
            [])
      | _, `TLS_1_2 ->
        if config.signature_algorithms = [] then
          Error (`Msg "TLS 1.2 configured but no signature algorithms provided")
        else begin
          Log.warn (fun m -> m "TLS 1.2 as maximum version configured, removing 1.3 cipher suites");
          Ok (List.filter
                (fun c -> not (Ciphersuite.ciphersuite_tls13 c)) config.ciphers,
              config.signature_algorithms)
      end
    | `TLS_1_3, `TLS_1_3 ->
      let sa = List.filter tls13_sigalg config.signature_algorithms in
      if sa = [] then
        Error (`Msg "TLS 1.3 configured but no 1.3 signature algorithms provided")
      else begin
        Log.warn (fun m -> m "only TLS 1.3 configured, removing pre-1.3 cipher suites and signature algorithms");
        Ok (List.filter Ciphersuite.ciphersuite_tls13 config.ciphers, sa)
      end
    | _ -> Ok (config.ciphers, config.signature_algorithms)
  in
  if not (Utils.List_set.is_proper_set ciphers) then
    Error (`Msg "set of ciphers is not a proper set")
  else if List.length ciphers = 0 then
    Error (`Msg "set of ciphers is empty")
  else if not (Utils.List_set.is_proper_set config.groups) then
    Error (`Msg "set of groups is not a proper set")
  else if not (Utils.List_set.is_proper_set signature_algorithms) then
    Error (`Msg "set of signature algorithms is not a proper set")
  else if List.exists (fun proto -> let len = String.length proto in len = 0 || len > 255) config.alpn_protocols then
    Error (`Msg "invalid alpn protocol")
  else if List.length config.alpn_protocols > 0xffff then
    Error (`Msg "alpn protocols list too large")
  else
    Ok { config with ciphers ; signature_algorithms }

let validate_certificate_chain = function
  | (s::chain, priv) ->
    let ( let* ) = Result.bind in
    let pub = X509.Private_key.public priv in
    let* () =
      match pub with
      | `RSA pub when Mirage_crypto_pk.Rsa.pub_bits pub < min_rsa_key_size ->
        Error (`Msg "RSA key too short!")
      | _ -> Ok ()
    in
    let* () =
      let eq_pub a b =
        String.equal (X509.Public_key.fingerprint a) (X509.Public_key.fingerprint b)
      in
      if not (eq_pub pub (X509.Certificate.public_key s)) then
        Error (`Msg "public / private key combination" )
      else
        Ok ()
    in
    ( match Utils.init_and_last chain with
      | Some (ch, trust) ->
        (* TODO: verify that certificates are x509 v3 if TLS_1_2 *)
        ( match X509.Validation.verify_chain_of_trust ~time:(fun () -> None) ~host:None ~anchors:[trust] (s :: ch) with
          | Ok _   -> Ok ()
          | Error x ->
            let s = Fmt.to_to_string X509.Validation.pp_validation_error x in
            Error (`Msg ("certificate chain does not validate: " ^ s)))
      | None -> Ok () )
  | _ -> Error (`Msg "certificate chain")

let validate_client config =
  match config.own_certificates with
  | `None -> Ok ()
  | `Single c -> validate_certificate_chain c
  | _ -> Error (`Msg "multiple client certificates not supported in client config")

let non_overlapping cs =
  let namessets =
    List.filter_map (function
        | (s :: _, _) -> Some s
        | _           -> None)
      cs
    |> List.map X509.Certificate.hostnames
  in
  let rec check = function
    | []    -> ()
    | s::ss ->
      if not (List.for_all (fun ss' ->
          X509.Host.Set.is_empty (X509.Host.Set.inter s ss'))
          ss)
      then
        invalid_arg "overlapping names in certificates"
      else
        check ss
  in
  check namessets

module KU = Set.Make (struct
    type t = X509.Extension.key_usage
    let compare a b = compare a b
  end)

module PK = Map.Make (struct
    type t = [ `RSA | `ED25519 | `P256 | `P384 | `P521 ]
    let compare a b = compare a b
  end)

let validate_server config =
  let ( let* ) = Result.bind in
  let open Ciphersuite in
  let usages =
    List.fold_left
      (fun acc c -> KU.add (required_usage (ciphersuite_kex c)) acc)
      KU.empty config.ciphers
  in
  let* certificate_chains =
    match config.own_certificates with
    | `Single c                 -> Ok [c]
    | `Multiple cs              -> Ok cs
    | `Multiple_default (c, cs) -> Ok (c :: cs)
    | `None                     -> Error (`Msg "no server certificate provided")
  in
  let* server_certs =
    List.fold_left (fun acc cc ->
        let* acc = acc in
        match cc with
        | (s::_,_) -> Ok (s :: acc)
        | _ -> Error (`Msg "empty certificate chain"))
      (Ok []) certificate_chains
  in
  let* () =
    if not
        (KU.for_all (fun u ->
             List.exists (supports_key_usage ~not_present:true u) server_certs)
            usages)
    then
      Error (`Msg "certificate usage does not match")
    else
      Ok ()
  in
  let* () =
    List.fold_left (fun acc cc ->
        let* () = acc in
        validate_certificate_chain cc)
      (Ok ()) certificate_chains
  in
  let rsa_cert, ec_cert =
    let is_ec_cert c = match X509.Certificate.public_key c with
      | `ED25519 _ | `P256 _ | `P384 _ | `P521 _ -> true
      | _ -> false
    and is_rsa_cert c = match X509.Certificate.public_key c with
      | `RSA _ -> true | _ -> false
    in
    List.exists is_rsa_cert server_certs,
    List.exists is_ec_cert server_certs
  in
  let ciphers =
    List.filter
      (function
        | #Ciphersuite.ciphersuite13 -> true
        | c ->
          let keytype = ciphersuite_keytype c in
          (rsa_cert && keytype = `RSA) || (ec_cert && keytype = `EC))
      config.ciphers
  in
  ( match config.own_certificates with
    | `Multiple cs
    | `Multiple_default (_, cs) ->
      let add k v acc = match PK.find_opt k acc with
        | None -> PK.add k [v] acc
        | Some r -> PK.add k (v :: r) acc
      in
      let pk =
        List.fold_left (fun acc cs ->
            match snd cs with
            | `RSA _ -> add `RSA cs acc
            | `ED25519 _ -> add `ED25519 cs acc
            | `P256 _ -> add `P256 cs acc
            | `P384 _ -> add `P384 cs acc
            | `P521 _ -> add `P521 cs acc)
          PK.empty cs
      in
      PK.iter (fun _ chains -> non_overlapping chains) pk
    | _ -> () );
  Ok { config with ciphers }

let validate_keys_sig_algs config =
  let ( let* ) = Result.bind in
  let _, v_max = config.protocol_versions in
  if v_max = `TLS_1_2 || v_max = `TLS_1_3 then
    let* certificate_chains =
      match config.own_certificates with
      | `Single c                 -> Ok [c]
      | `Multiple cs              -> Ok cs
      | `Multiple_default (c, cs) -> Ok (c :: cs)
      | `None                     -> Error (`Msg "no server certificate provided")
    in
    let* server_keys =
      List.fold_left (fun acc cc ->
          let* acc = acc in
          match cc with
          | (s::_,_) -> Ok (X509.Certificate.public_key s :: acc)
          | _ -> Error (`Msg "empty certificate chain"))
        (Ok []) certificate_chains
    in
    if not
        (List.for_all (fun cert ->
             List.exists (pk_matches_sa cert) config.signature_algorithms)
            server_keys)
    then
      Error (`Msg "certificate provided which does not allow any signature algorithm")
    else
      Ok ()
  else
    Ok ()

type client = config
type server = config

let of_server conf = conf
and of_client conf = conf

let peer conf name = { conf with peer_name = Some name }

let with_authenticator conf auth = { conf with authenticator = Some auth }

let with_own_certificates conf own_certificates = { conf with own_certificates }

let with_acceptable_cas conf acceptable_cas = { conf with acceptable_cas }

let (<?>) ma b = match ma with None -> b | Some a -> a

let client
    ~authenticator ?peer_name ?ciphers ?version ?signature_algorithms ?reneg ?certificates ?cached_session ?cached_ticket ?ticket_cache ?alpn_protocols ?groups ?ip () =
  let ( let* ) = Result.bind in
  let* ciphers', groups = ciphers_and_groups ?ciphers ?groups default_config.ciphers in
  let* ciphers, signature_algorithms = ciphers_and_sig_alg ?ciphers ?signature_algorithms ciphers' in
  let config =
    { default_config with
        authenticator = Some authenticator ;
        ciphers ;
        protocol_versions = version <?> default_config.protocol_versions ;
        signature_algorithms ;
        use_reneg = reneg <?> default_config.use_reneg ;
        own_certificates  = certificates <?> default_config.own_certificates ;
        peer_name = peer_name ;
        cached_session = cached_session ;
        alpn_protocols = alpn_protocols <?> default_config.alpn_protocols ;
        ticket_cache = ticket_cache ;
        cached_ticket = cached_ticket ;
        groups ;
        ip ;
    } in
  let* config = validate_common config in
  let* () = validate_client config in
  Log.debug (fun m -> m "client with %a" pp_config config);
  Ok config

let server
    ?ciphers ?version ?signature_algorithms ?reneg ?certificates ?acceptable_cas ?authenticator ?session_cache ?ticket_cache ?alpn_protocols ?groups ?zero_rtt ?ip () =
  let ( let* ) = Result.bind in
  let* ciphers', groups = ciphers_and_groups ?ciphers ?groups default_config.ciphers in
  let* ciphers, signature_algorithms = ciphers_and_sig_alg ?ciphers ?signature_algorithms ciphers' in
  let config =
    { default_config with
        ciphers ;
        protocol_versions = version <?> default_config.protocol_versions ;
        signature_algorithms ;
        use_reneg = reneg <?> default_config.use_reneg ;
        own_certificates = certificates <?> default_config.own_certificates ;
        acceptable_cas = acceptable_cas <?> default_config.acceptable_cas ;
        authenticator = authenticator ;
        session_cache = session_cache  <?> default_config.session_cache ;
        alpn_protocols = alpn_protocols <?> default_config.alpn_protocols ;
        ticket_cache = ticket_cache ;
        groups ;
        zero_rtt = zero_rtt <?> default_config.zero_rtt ;
        ip ;
    } in
  let* config = validate_server config in
  let* config = validate_common config in
  let* () = validate_keys_sig_algs config in
  Log.debug (fun m -> m "server with %a" pp_config config);
  Ok config