crypto: switch JWT JSON to simdjsont

.beads/issues.jsonl

···
 {"id":"atproto-52","title":"Implement Lexicon validation","description":"Implement Lexicon-based validation for AT Protocol data. This validates records and API payloads against schemas.","design":"## Module Structure\n\n```ocaml\n(* atproto-lexicon/lib/validator.ml *)\ntype validation_error = {\n  path: string list;\n  message: string;\n}\n\nval validate_record :\n  registry:Registry.t -\u003e\n  nsid:Nsid.t -\u003e\n  value:Dag_cbor.value -\u003e\n  (unit, validation_error list) result\n\nval validate_xrpc_params :\n  registry:Registry.t -\u003e\n  nsid:Nsid.t -\u003e\n  params:(string * string) list -\u003e\n  (unit, validation_error list) result\n\nval validate_xrpc_input :\n  registry:Registry.t -\u003e\n  nsid:Nsid.t -\u003e\n  input:Jsont.json -\u003e\n  (unit, validation_error list) result\n\nval validate_xrpc_output :\n  registry:Registry.t -\u003e\n  nsid:Nsid.t -\u003e\n  output:Jsont.json -\u003e\n  (unit, validation_error list) result\n```\n\n## Constraint Types\n\n- **String**: minLength, maxLength, minGraphemes, maxGraphemes, format, enum, const\n- **Integer**: minimum, maximum, enum, const\n- **Bytes**: minLength, maxLength\n- **Array**: minLength, maxLength, items type\n- **Blob**: maxSize, accept (MIME types)\n- **Union**: open/closed, refs\n\n## Format Validators (Parser-based, NO REGEX)\n\nEach format has a dedicated parser module:\n\n```ocaml\n(* atproto-lexicon/lib/formats.ml *)\n\nlet validate_did s = Did.of_string s |\u003e Result.is_ok\nlet validate_handle s = Handle.of_string s |\u003e Result.is_ok\nlet validate_nsid s = Nsid.of_string s |\u003e Result.is_ok\nlet validate_tid s = Tid.of_string s |\u003e Result.is_ok\nlet validate_cid s = Cid.of_string s |\u003e Result.is_ok\nlet validate_at_uri s = At_uri.of_string s |\u003e Result.is_ok\nlet validate_at_identifier s = \n  Did.of_string s |\u003e Result.is_ok || Handle.of_string s |\u003e Result.is_ok\nlet validate_record_key s = Record_key.of_string s |\u003e Result.is_ok\n\nlet validate_datetime s =\n  (* Hand-written RFC-3339 parser *)\n  parse_datetime s |\u003e Result.is_ok\n\nlet validate_language s =\n  (* BCP-47 language tag parser *)\n  parse_language_tag s |\u003e Result.is_ok\n\nlet validate_uri s =\n  (* RFC-3986 URI parser *)\n  Uri.of_string s |\u003e Option.is_some\n```\n\n## Dependencies\n- atproto-lexicon (schema)\n- atproto-syntax (format validators)\n- jsont","acceptance_criteria":"- Validate records against schemas\n- Validate XRPC params, input, output\n- Proper error messages with paths\n- All constraint types supported\n- All record-data interop tests pass","status":"closed","priority":1,"issue_type":"feature","assignee":"claude","created_at":"2025-12-28T00:11:39.125440686+01:00","updated_at":"2025-12-28T10:25:46.671434007+01:00","closed_at":"2025-12-28T10:25:46.671434007+01:00","labels":["application","lexicon"],"dependencies":[{"issue_id":"atproto-52","depends_on_id":"atproto-50","type":"parent-child","created_at":"2025-12-28T00:12:05.375287273+01:00","created_by":"daemon"},{"issue_id":"atproto-52","depends_on_id":"atproto-51","type":"blocks","created_at":"2025-12-28T00:12:09.479940241+01:00","created_by":"daemon"}]}
 {"id":"atproto-53","title":"Implement Lexicon code generation","description":"Implement code generation from Lexicon schemas to OCaml types and API bindings.","design":"## Module Structure\n\n```ocaml\n(* atproto-lexicon-gen/lib/codegen.ml *)\ntype config = {\n  output_dir: string;\n  module_prefix: string;\n}\n\nval generate_types : config:config -\u003e lexicon:Lexicon.t -\u003e unit\nval generate_client : config:config -\u003e lexicons:Lexicon.t list -\u003e unit\n```\n\n## Generated Code Example\n\nInput Lexicon:\n```json\n{\n  \"id\": \"app.bsky.feed.post\",\n  \"defs\": {\n    \"main\": {\n      \"type\": \"record\",\n      \"record\": {\n        \"type\": \"object\",\n        \"properties\": {\n          \"text\": { \"type\": \"string\", \"maxGraphemes\": 300 },\n          \"createdAt\": { \"type\": \"string\", \"format\": \"datetime\" }\n        }\n      }\n    }\n  }\n}\n```\n\nGenerated OCaml:\n```ocaml\nmodule App_bsky_feed_post = struct\n  type t = {\n    text: string;\n    created_at: Ptime.t;\n  }\n  \n  let jsont : t Jsont.t =\n    Jsont.obj \"app.bsky.feed.post\" @@ fun o -\u003e\n    let text = Jsont.obj_mem o \"text\" Jsont.string in\n    let created_at = Jsont.obj_mem o \"createdAt\" Datetime.jsont in\n    Jsont.obj_finish o { text; created_at }\n  \n  val to_dag_cbor : t -\u003e Dag_cbor.value\n  val of_dag_cbor : Dag_cbor.value -\u003e (t, error) result\nend\n```\n\n## CLI Tool\n\n```bash\natproto-lexicon-gen --input lexicons/ --output lib/generated/\n```\n\n## Dependencies\n- atproto-lexicon\n- jsont","acceptance_criteria":"- Generate OCaml types from Lexicon schemas\n- Generate encoders/decoders\n- Type-safe API bindings\n- CLI tool for code generation","status":"closed","priority":2,"issue_type":"feature","assignee":"claude","created_at":"2025-12-28T00:11:47.861552784+01:00","updated_at":"2025-12-28T11:28:03.226633204+01:00","closed_at":"2025-12-28T11:28:03.226633204+01:00","labels":["application","codegen"],"dependencies":[{"issue_id":"atproto-53","depends_on_id":"atproto-50","type":"parent-child","created_at":"2025-12-28T00:12:06.539440409+01:00","created_by":"daemon"},{"issue_id":"atproto-53","depends_on_id":"atproto-51","type":"blocks","created_at":"2025-12-28T00:12:11.189125052+01:00","created_by":"daemon"}]}
 {"id":"atproto-54","title":"Implement high-level API client","description":"Implement high-level API client for AT Protocol / Bluesky. This provides a user-friendly interface for common operations.","design":"## Module Structure\n\n```ocaml\n(* atproto-api/lib/agent.ml *)\ntype t\n\nval create : pds:Uri.t -\u003e t\n\n(* Authentication *)\nval login : t -\u003e identifier:string -\u003e password:string -\u003e (t, error) result\nval login_oauth : t -\u003e tokens:Oauth.tokens -\u003e t\nval refresh_session : t -\u003e (t, error) result\n\n(* Profile *)\nval get_profile : t -\u003e actor:string -\u003e (profile, error) result\nval update_profile : t -\u003e display_name:string option -\u003e ... -\u003e (unit, error) result\n\n(* Posts *)\nval create_post : t -\u003e text:string -\u003e ?reply:reply_ref -\u003e ... -\u003e (post_ref, error) result\nval delete_post : t -\u003e uri:At_uri.t -\u003e (unit, error) result\n\n(* Social *)\nval like : t -\u003e uri:At_uri.t -\u003e cid:Cid.t -\u003e (like_ref, error) result\nval follow : t -\u003e did:Did.t -\u003e (follow_ref, error) result\nval unfollow : t -\u003e uri:At_uri.t -\u003e (unit, error) result\n\n(* Feed *)\nval get_timeline : t -\u003e ?cursor:string -\u003e ?limit:int -\u003e (timeline, error) result\nval get_author_feed : t -\u003e actor:string -\u003e ... -\u003e (feed, error) result\n\n(* atproto-api/lib/richtext.ml *)\ntype t\n\nval create : string -\u003e t\nval detect_facets : t -\u003e t  (* auto-detect mentions, links *)\nval add_mention : t -\u003e start:int -\u003e end_:int -\u003e did:Did.t -\u003e t\nval add_link : t -\u003e start:int -\u003e end_:int -\u003e uri:Uri.t -\u003e t\nval to_post_record : t -\u003e Dag_cbor.value\n```\n\n## Jsont Codecs for API Types\n\n```ocaml\nlet profile_jsont : profile Jsont.t =\n  Jsont.obj \"profile\" @@ fun o -\u003e\n  let did = Jsont.obj_mem o \"did\" did_jsont in\n  let handle = Jsont.obj_mem o \"handle\" handle_jsont in\n  let display_name = Jsont.obj_mem o \"displayName\" ~opt:true Jsont.string in\n  let description = Jsont.obj_mem o \"description\" ~opt:true Jsont.string in\n  let avatar = Jsont.obj_mem o \"avatar\" ~opt:true Jsont.string in\n  let followers_count = Jsont.obj_mem o \"followersCount\" ~opt:true Jsont.int in\n  let follows_count = Jsont.obj_mem o \"followsCount\" ~opt:true Jsont.int in\n  let posts_count = Jsont.obj_mem o \"postsCount\" ~opt:true Jsont.int in\n  Jsont.obj_finish o { did; handle; display_name; description; avatar; \n                        followers_count; follows_count; posts_count }\n\nlet facet_jsont : facet Jsont.t =\n  Jsont.obj \"facet\" @@ fun o -\u003e\n  let index = Jsont.obj_mem o \"index\" byte_slice_jsont in\n  let features = Jsont.obj_mem o \"features\" (Jsont.list facet_feature_jsont) in\n  Jsont.obj_finish o { index; features }\n```\n\n## RichText Facets\n\n```json\n{\n  \"text\": \"Hello @alice.bsky.social!\",\n  \"facets\": [\n    {\n      \"index\": { \"byteStart\": 6, \"byteEnd\": 25 },\n      \"features\": [\n        { \"$type\": \"app.bsky.richtext.facet#mention\", \"did\": \"did:plc:...\" }\n      ]\n    }\n  ]\n}\n```\n\n## Dependencies\n- atproto-xrpc\n- atproto-identity\n- atproto-repo\n- jsont","acceptance_criteria":"- Session management (login, logout, refresh)\n- Common operations (post, like, follow, etc.)\n- RichText handling (mentions, links, facets)\n- Timeline and feed fetching\n- Profile operations","status":"closed","priority":2,"issue_type":"feature","assignee":"claude","created_at":"2025-12-28T00:12:00.736309435+01:00","updated_at":"2025-12-28T11:47:47.071271001+01:00","closed_at":"2025-12-28T11:47:47.071271001+01:00","labels":["api","application"],"dependencies":[{"issue_id":"atproto-54","depends_on_id":"atproto-50","type":"parent-child","created_at":"2025-12-28T00:12:07.636789403+01:00","created_by":"daemon"},{"issue_id":"atproto-54","depends_on_id":"atproto-41","type":"blocks","created_at":"2025-12-28T00:12:12.376875324+01:00","created_by":"daemon"},{"issue_id":"atproto-54","depends_on_id":"atproto-33","type":"blocks","created_at":"2025-12-28T00:12:13.060557136+01:00","created_by":"daemon"},{"issue_id":"atproto-54","depends_on_id":"atproto-25","type":"blocks","created_at":"2025-12-28T00:12:13.934360048+01:00","created_by":"daemon"}]}
-{"id":"atproto-5l1","title":"Refactor JSON to simdjsont (replace yojson/jsont)","description":"","notes":"Proceeding with simdjsont 0.1.0 migration. Plan: introduce atproto_json wrapper using Simdjsont.Json.t + Simdjsont.Codec; migrate public APIs off Yojson.*.t; update dune/opam deps; keep tests green incrementally.","status":"in_progress","priority":1,"issue_type":"feature","created_at":"2026-01-01T18:06:10.17746938+01:00","updated_at":"2026-01-01T19:00:19.875102367+01:00","dependencies":[{"issue_id":"atproto-5l1","depends_on_id":"atproto-dqs","type":"blocks","created_at":"2026-01-01T18:06:39.648046004+01:00","created_by":"daemon"}]}
+{"id":"atproto-5l1","title":"Refactor JSON to simdjsont (replace yojson/jsont)","description":"","notes":"Next steps: migrate lib/crypto/jwt.ml off Yojson.Safe to Atproto_json/Simdjsont.Json (header_to_json/claims_to_json + *_of_json + create/decode_unverified); add atproto-json to lib/crypto/dune; run dune runtest test/crypto + full runtest; then continue with other Yojson hotspots (xrpc client/server, identity did_resolver, sync firehose, ipld blob).","status":"in_progress","priority":1,"issue_type":"feature","created_at":"2026-01-01T18:06:10.17746938+01:00","updated_at":"2026-01-01T19:32:47.437650903+01:00","dependencies":[{"issue_id":"atproto-5l1","depends_on_id":"atproto-dqs","type":"blocks","created_at":"2026-01-01T18:06:39.648046004+01:00","created_by":"daemon"}]}
 {"id":"atproto-60","title":"Implement effects-based I/O abstraction","description":"Implement the effects-based I/O abstraction layer that makes all libraries runtime-agnostic.","design":"## Module Structure\n\n```ocaml\n(* atproto-effects/lib/effects.ml *)\n\n(* HTTP effects *)\ntype http_request = {\n  method_: [ `GET | `POST | `PUT | `DELETE ];\n  uri: Uri.t;\n  headers: (string * string) list;\n  body: string option;\n}\n\ntype http_response = {\n  status: int;\n  headers: (string * string) list;\n  body: string;\n}\n\ntype _ Effect.t +=\n  | Http_request : http_request -\u003e http_response Effect.t\n\n(* DNS effects *)\ntype _ Effect.t +=\n  | Dns_txt : string -\u003e string list Effect.t\n  | Dns_a : string -\u003e string list Effect.t\n\n(* Time effects *)\ntype _ Effect.t +=\n  | Now : Ptime.t Effect.t\n  | Sleep : float -\u003e unit Effect.t\n\n(* Random effects *)\ntype _ Effect.t +=\n  | Random_bytes : int -\u003e bytes Effect.t\n\n(* atproto-effects-eio/lib/handler.ml *)\nval run : (unit -\u003e 'a) -\u003e 'a\n```\n\n## Handler Example (eio)\n\n```ocaml\nlet run f =\n  Effect.Deep.match_ f ()\n  {\n    retc = Fun.id;\n    exnc = raise;\n    effc = fun (type a) (e : a Effect.t) -\u003e\n      match e with\n      | Http_request req -\u003e\n        Some (fun (k : (a, _) continuation) -\u003e\n          let resp = Eio_client.request req in\n          continue k resp)\n      | Dns_txt domain -\u003e\n        Some (fun k -\u003e\n          let records = Eio_dns.txt domain in\n          continue k records)\n      | _ -\u003e None\n  }\n```\n\n## Dependencies\n- eio (for testing handler)","acceptance_criteria":"- Effect types for HTTP, DNS, time, random\n- eio-based handler for testing\n- Handler composition utilities\n- Performance benchmarks","status":"closed","priority":1,"issue_type":"feature","assignee":"claude","created_at":"2025-12-28T00:12:29.021401617+01:00","updated_at":"2025-12-28T11:57:08.264086142+01:00","closed_at":"2025-12-28T11:57:08.264086142+01:00","labels":["effects","infrastructure"],"dependencies":[{"issue_id":"atproto-60","depends_on_id":"atproto-1","type":"parent-child","created_at":"2025-12-28T00:12:55.467983208+01:00","created_by":"daemon"}]}
 {"id":"atproto-61","title":"Set up interoperability test suite","description":"Set up and run the AT Protocol interoperability tests from bluesky-social/atproto-interop-tests.","design":"## Test Structure\n\n```\ntest/\n├── interop/\n│   ├── syntax_test.ml      # Handle, DID, NSID, TID, etc.\n│   ├── crypto_test.ml      # Signatures, did:key\n│   ├── data_model_test.ml  # DAG-CBOR, CID\n│   ├── mst_test.ml         # Key heights, tree structure\n│   ├── lexicon_test.ml     # Schema and record validation\n│   └── firehose_test.ml    # Commit proofs\n├── fixtures/               # Cloned from atproto-interop-tests\n└── dune\n```\n\n## Test Approach\n\n1. Clone test vectors from GitHub\n2. Parse JSON fixtures using jsont\n3. Parse text fixtures line by line\n4. Run each test case\n5. Compare output to expected values\n\n## Example Test\n\n```ocaml\nlet load_json_fixtures path =\n  let json = Jsont.of_file path in\n  Jsont.decode (Jsont.list fixture_jsont) json\n\nlet%test \"handle_syntax_valid\" =\n  let fixtures = load_lines \"fixtures/syntax/handle_syntax_valid.txt\" in\n  List.for_all (fun line -\u003e\n    match Handle.of_string line with\n    | Ok _ -\u003e true\n    | Error _ -\u003e false\n  ) fixtures\n\nlet%test \"handle_syntax_invalid\" =\n  let fixtures = load_lines \"fixtures/syntax/handle_syntax_invalid.txt\" in\n  List.for_all (fun line -\u003e\n    match Handle.of_string line with\n    | Ok _ -\u003e false\n    | Error _ -\u003e true\n  ) fixtures\n\nlet%test \"crypto_signature_fixtures\" =\n  let fixtures = load_json_fixtures \"fixtures/crypto/signature-fixtures.json\" in\n  List.for_all (fun fixture -\u003e\n    let message = Base64.decode fixture.message_base64 in\n    let signature = Base64.decode fixture.signature_base64 in\n    let key = Did_key.of_string fixture.public_key_did in\n    let result = Crypto.verify key message signature in\n    result = fixture.valid_signature\n  ) fixtures\n```\n\n## Dependencies\n- alcotest or ounit2\n- jsont","acceptance_criteria":"- All syntax interop tests pass\n- All crypto interop tests pass\n- All data-model interop tests pass\n- All MST interop tests pass\n- All lexicon interop tests pass\n- All firehose interop tests pass","status":"closed","priority":1,"issue_type":"task","created_at":"2025-12-28T00:12:40.553908313+01:00","updated_at":"2025-12-28T13:25:34.614867702+01:00","closed_at":"2025-12-28T13:25:34.614867702+01:00","labels":["conformance","testing"],"dependencies":[{"issue_id":"atproto-61","depends_on_id":"atproto-1","type":"parent-child","created_at":"2025-12-28T00:12:56.180809368+01:00","created_by":"daemon"}]}
 {"id":"atproto-62","title":"Set up monorepo package structure","description":"Set up the monorepo structure for multiple opam packages within a single repository.","design":"## Repository Structure\n\n```\natproto/\n├── dune-project           # Root with all packages\n├── packages/\n│   ├── atproto-syntax/\n│   │   ├── lib/\n│   │   │   ├── dune\n│   │   │   └── *.ml\n│   │   ├── test/\n│   │   │   ├── dune\n│   │   │   └── *_test.ml\n│   │   └── atproto-syntax.opam\n│   ├── atproto-crypto/\n│   ├── atproto-multibase/\n│   ├── atproto-ipld/\n│   ├── atproto-mst/\n│   ├── atproto-repo/\n│   ├── atproto-identity/\n│   ├── atproto-xrpc/\n│   ├── atproto-sync/\n│   ├── atproto-lexicon/\n│   ├── atproto-lexicon-gen/\n│   ├── atproto-api/\n│   └── atproto-effects/\n├── examples/\n│   ├── simple_client/\n│   └── firehose_consumer/\n└── interop-tests/\n```\n\n## dune-project\n\n```lisp\n(lang dune 3.20)\n(name atproto)\n(generate_opam_files true)\n\n(package\n (name atproto-syntax)\n (synopsis \"AT Protocol identifier syntax parsing\")\n (depends\n  (ocaml (\u003e= 5.4))\n  re\n  ptime))\n\n(package\n (name atproto-crypto)\n ...)\n```\n\n## CI (.github/workflows/ci.yml)\n\n- OCaml 5.4 matrix\n- Build all packages\n- Run all tests\n- Run interop tests","acceptance_criteria":"- Multi-package dune-project structure\n- Separate opam files per package\n- CI pipeline for building and testing\n- Documentation generation setup","status":"closed","priority":1,"issue_type":"task","created_at":"2025-12-28T00:12:50.547102438+01:00","updated_at":"2025-12-28T11:57:18.856810633+01:00","closed_at":"2025-12-28T11:57:18.856810633+01:00","labels":["infrastructure","setup"],"dependencies":[{"issue_id":"atproto-62","depends_on_id":"atproto-1","type":"parent-child","created_at":"2025-12-28T00:12:57.015938611+01:00","created_by":"daemon"}]}

lib/crypto/dune

···
 (library
  (name atproto_crypto)
  (public_name atproto-crypto)
- (libraries atproto_multibase mirage-crypto-ec mirage-crypto-rng digestif zarith base64 yojson)
+ (libraries atproto_multibase mirage-crypto-ec mirage-crypto-rng digestif zarith base64 yojson simdjsont)
  (preprocess no_preprocessing))

lib/crypto/jwt.ml

···
   | "ES256K" -> Ok ES256K
   | alg -> Error (`Unsupported_algorithm alg)
 
-let header_to_json (h : header) : Yojson.Safe.t =
-  `Assoc
-    [ ("alg", `String (algorithm_to_string h.alg)); ("typ", `String h.typ) ]
+type json = Simdjsont.Json.t
 
-let header_of_json (json : Yojson.Safe.t) : (header, error) result =
+let header_to_json (h : header) : json =
+  Simdjsont.Json.Object
+    [
+      ("alg", Simdjsont.Json.String (algorithm_to_string h.alg));
+      ("typ", Simdjsont.Json.String h.typ);
+    ]
+
+let header_of_json (json : json) : (header, error) result =
   match json with
-  | `Assoc pairs -> (
+  | Simdjsont.Json.Object pairs -> (
       let get_string key =
         match List.assoc_opt key pairs with
-        | Some (`String s) -> Some s
+        | Some (Simdjsont.Json.String s) -> Some s
         | _ -> None
       in
       match get_string "alg" with
···
               | Some typ -> Ok { alg; typ })))
   | _ -> Error (`Invalid_json "header must be an object")
 
-let claims_to_json (c : claims) : Yojson.Safe.t =
+let claims_to_json (c : claims) : json =
   let fields =
     [
-      ("iss", `String c.iss);
-      ("aud", `String c.aud);
-      ("exp", `Int (Int64.to_int c.exp));
-      ("iat", `Int (Int64.to_int c.iat));
+      ("iss", Simdjsont.Json.String c.iss);
+      ("aud", Simdjsont.Json.String c.aud);
+      ("exp", Simdjsont.Json.Int c.exp);
+      ("iat", Simdjsont.Json.Int c.iat);
     ]
   in
   let add_opt key = function
     | None -> Fun.id
-    | Some v -> fun acc -> (key, `String v) :: acc
+    | Some v -> fun acc -> (key, Simdjsont.Json.String v) :: acc
   in
   let fields =
     fields |> add_opt "sub" c.sub |> add_opt "jti" c.jti |> add_opt "lxm" c.lxm
     |> add_opt "nonce" c.nonce |> add_opt "scope" c.scope
   in
-  `Assoc fields
+  Simdjsont.Json.Object fields
 
-let claims_of_json (json : Yojson.Safe.t) : (claims, error) result =
+let claims_of_json (json : json) : (claims, error) result =
   match json with
-  | `Assoc pairs -> (
+  | Simdjsont.Json.Object pairs -> (
       let get_string key =
         match List.assoc_opt key pairs with
-        | Some (`String s) -> Some s
+        | Some (Simdjsont.Json.String s) -> Some s
         | _ -> None
       in
-      let get_int key =
+      let get_int64 key =
         match List.assoc_opt key pairs with
-        | Some (`Int i) -> Some (Int64.of_int i)
-        | Some (`Intlit s) -> ( try Some (Int64.of_string s) with _ -> None)
+        | Some (Simdjsont.Json.Int i) -> Some i
         | _ -> None
       in
       match
-        (get_string "iss", get_string "aud", get_int "exp", get_int "iat")
+        (get_string "iss", get_string "aud", get_int64 "exp", get_int64 "iat")
       with
       | Some iss, Some aud, Some exp, Some iat ->
           Ok
···
 let create ~(key : signing_key) ~(typ : string) ~(claims : claims) : t =
   let alg = match key with P256_key _ -> ES256 | K256_key _ -> ES256K in
   let header = { alg; typ } in
-  let header_json = Yojson.Safe.to_string (header_to_json header) in
-  let claims_json = Yojson.Safe.to_string (claims_to_json claims) in
+  let header_json =
+    Simdjsont.encode Simdjsont.Codec.value (header_to_json header)
+  in
+  let claims_json =
+    Simdjsont.encode Simdjsont.Codec.value (claims_to_json claims)
+  in
   let header_b64 = base64url_encode header_json in
   let claims_b64 = base64url_encode claims_json in
   let signing_input = header_b64 ^ "." ^ claims_b64 in
···
               | Error _ -> Error `Invalid_base64
               | Ok signature -> (
                   let header_json =
-                    try Ok (Yojson.Safe.from_string header_str)
-                    with Yojson.Json_error msg -> Error (`Invalid_json msg)
+                    match Simdjsont.decode Simdjsont.Codec.value header_str with
+                    | Ok v -> Ok v
+                    | Error msg -> Error (`Invalid_json msg)
                   in
                   let claims_json =
-                    try Ok (Yojson.Safe.from_string claims_str)
-                    with Yojson.Json_error msg -> Error (`Invalid_json msg)
+                    match Simdjsont.decode Simdjsont.Codec.value claims_str with
+                    | Ok v -> Ok v
+                    | Error msg -> Error (`Invalid_json msg)
                   in
                   match (header_json, claims_json) with
                   | Error e, _ -> Error e