feat(signup): add Gleam signup service gated by shared invite code

A small Gleam HTTP server in signup/ exposes POST /signup that validates
a shared INVITE_CODE env var, then PUTs a user document to CouchDB's
_users database using the existing admin credentials. The frontend gets
back 201 + the username and is expected to call /_session itself to
obtain the AuthSession cookie (chosen over server-side cookie forwarding
because vaquant.at and couch.apoena.dev are different sites and the
cross-site cookie path is fragile under modern browser privacy modes).

Wired into docker-compose as a second service, reachable on
signup-couch.apoena.dev with its own Traefik labels and the same
hardcoded UUID network attachment as couchdb. Reuses COUCHDB_USER /
COUCHDB_PASSWORD for the admin call. INVITE_CODE must be set in Coolify
env vars.

signup/.dockerignore

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+build/
+.git/
+*.beam

signup/Dockerfile

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+FROM ghcr.io/gleam-lang/gleam:v1.7.0-erlang-alpine AS builder
+WORKDIR /build
+COPY gleam.toml ./
+RUN gleam deps download
+COPY src ./src
+RUN gleam export erlang-shipment
+
+FROM erlang:27-alpine
+RUN apk add --no-cache openssl-dev
+WORKDIR /app
+COPY --from=builder /build/build/erlang-shipment .
+EXPOSE 8080
+ENTRYPOINT ["/app/entrypoint.sh", "run"]

signup/gleam.toml

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+name = "coolcouch_signup"
+version = "0.1.0"
+target = "erlang"
+
+[dependencies]
+gleam_stdlib = ">= 0.59.0 and < 2.0.0"
+gleam_http = ">= 4.0.0 and < 5.0.0"
+gleam_httpc = ">= 4.0.0 and < 5.0.0"
+gleam_json = ">= 3.0.0 and < 4.0.0"
+gleam_erlang = ">= 1.0.0 and < 2.0.0"
+envoy = ">= 1.0.0 and < 2.0.0"
+mist = ">= 4.0.0 and < 6.0.0"
+wisp = ">= 1.6.0 and < 2.0.0"

signup/src/coolcouch_signup.gleam

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+import envoy
+import gleam/bit_array
+import gleam/dynamic/decode
+import gleam/erlang/process
+import gleam/http.{Get, Options, Post}
+import gleam/http/request
+import gleam/http/response
+import gleam/httpc
+import gleam/int
+import gleam/io
+import gleam/json
+import gleam/list
+import gleam/option.{type Option, None, Some}
+import gleam/result
+import gleam/string
+import mist
+import wisp.{type Request, type Response}
+import wisp/wisp_mist
+
+pub type Config {
+  Config(
+    couchdb_url: String,
+    admin_user: String,
+    admin_password: String,
+    invite_code: String,
+    allowed_origins: List(String),
+    port: Int,
+  )
+}
+
+pub type SignupBody {
+  SignupBody(username: String, password: String, invite_code: String)
+}
+
+pub fn main() {
+  wisp.configure_logger()
+  let config = case load_config() {
+    Ok(c) -> c
+    Error(msg) -> {
+      io.println_error("config error: " <> msg)
+      panic as "missing required configuration"
+    }
+  }
+  let secret = wisp.random_string(64)
+  let assert Ok(_) =
+    wisp_mist.handler(fn(req) { handle_request(req, config) }, secret)
+    |> mist.new
+    |> mist.port(config.port)
+    |> mist.bind("0.0.0.0")
+    |> mist.start
+  io.println("coolcouch-signup listening on " <> int.to_string(config.port))
+  process.sleep_forever()
+}
+
+fn load_config() -> Result(Config, String) {
+  use admin_password <- result.try(
+    envoy.get("COUCHDB_ADMIN_PASSWORD")
+    |> result.replace_error("missing COUCHDB_ADMIN_PASSWORD"),
+  )
+  use invite_code <- result.try(
+    envoy.get("INVITE_CODE")
+    |> result.replace_error("missing INVITE_CODE"),
+  )
+  let couchdb_url =
+    envoy.get("COUCHDB_URL") |> result.unwrap("http://couchdb:5984")
+  let admin_user = envoy.get("COUCHDB_ADMIN_USER") |> result.unwrap("admin")
+  let allowed_origins =
+    envoy.get("SIGNUP_ALLOWED_ORIGINS")
+    |> result.unwrap("")
+    |> string.split(",")
+    |> list.map(string.trim)
+    |> list.filter(fn(s) { s != "" })
+  let port =
+    envoy.get("PORT")
+    |> result.try(fn(p) {
+      int.parse(p) |> result.replace_error(Nil)
+    })
+    |> result.unwrap(8080)
+  Ok(Config(
+    couchdb_url: couchdb_url,
+    admin_user: admin_user,
+    admin_password: admin_password,
+    invite_code: invite_code,
+    allowed_origins: allowed_origins,
+    port: port,
+  ))
+}
+
+fn handle_request(req: Request, config: Config) -> Response {
+  let allow_origin = case request.get_header(req, "origin") {
+    Ok(origin) ->
+      case list.contains(config.allowed_origins, origin) {
+        True -> Some(origin)
+        False -> None
+      }
+    Error(_) -> None
+  }
+  case req.method, wisp.path_segments(req) {
+    Options, _ -> preflight(allow_origin)
+    Get, ["health"] -> with_cors(wisp.ok(), allow_origin)
+    Post, ["signup"] -> with_cors(handle_signup(req, config), allow_origin)
+    _, _ -> with_cors(wisp.not_found(), allow_origin)
+  }
+}
+
+fn preflight(allow_origin: Option(String)) -> Response {
+  let base =
+    wisp.response(204)
+    |> wisp.set_header("access-control-allow-methods", "POST, OPTIONS")
+    |> wisp.set_header("access-control-allow-headers", "content-type")
+    |> wisp.set_header("access-control-max-age", "600")
+    |> wisp.set_header("vary", "Origin")
+  case allow_origin {
+    Some(origin) -> wisp.set_header(base, "access-control-allow-origin", origin)
+    None -> base
+  }
+}
+
+fn with_cors(resp: Response, allow_origin: Option(String)) -> Response {
+  case allow_origin {
+    Some(origin) ->
+      resp
+      |> wisp.set_header("access-control-allow-origin", origin)
+      |> wisp.set_header("vary", "Origin")
+    None -> resp
+  }
+}
+
+fn handle_signup(req: Request, config: Config) -> Response {
+  use body <- wisp.require_json(req)
+  let decoder = {
+    use username <- decode.field("username", decode.string)
+    use password <- decode.field("password", decode.string)
+    use invite_code <- decode.field("invite_code", decode.string)
+    decode.success(SignupBody(username:, password:, invite_code:))
+  }
+  case decode.run(body, decoder) {
+    Error(_) -> error_json(400, "invalid_payload")
+    Ok(SignupBody(username, password, invite_code)) ->
+      validate_and_create(config, username, password, invite_code)
+  }
+}
+
+fn validate_and_create(
+  config: Config,
+  username: String,
+  password: String,
+  invite_code: String,
+) -> Response {
+  case invite_code == config.invite_code {
+    False -> error_json(401, "invalid_invite_code")
+    True ->
+      case valid_username(username), string.length(password) >= 8 {
+        False, _ -> error_json(400, "invalid_username")
+        _, False -> error_json(400, "password_too_short")
+        True, True -> create_user(config, username, password)
+      }
+  }
+}
+
+fn valid_username(name: String) -> Bool {
+  let len = string.length(name)
+  len >= 1 && len <= 64 && string.to_graphemes(name) |> list.all(allowed_char)
+}
+
+fn allowed_char(c: String) -> Bool {
+  case c {
+    "-" | "_" | "." -> True
+    _ ->
+      // letters and digits only (basic ASCII range)
+      case string.to_utf_codepoints(c) {
+        [cp] -> {
+          let n = string.utf_codepoint_to_int(cp)
+          { n >= 0x30 && n <= 0x39 }
+          || { n >= 0x41 && n <= 0x5A }
+          || { n >= 0x61 && n <= 0x7A }
+        }
+        _ -> False
+      }
+  }
+}
+
+fn create_user(config: Config, username: String, password: String) -> Response {
+  let doc =
+    json.object([
+      #("_id", json.string("org.couchdb.user:" <> username)),
+      #("name", json.string(username)),
+      #("type", json.string("user")),
+      #("roles", json.array([], json.string)),
+      #("password", json.string(password)),
+    ])
+    |> json.to_string
+  let url =
+    config.couchdb_url <> "/_users/org.couchdb.user:" <> username
+  let assert Ok(base_req) = request.to(url)
+  let req =
+    base_req
+    |> request.set_method(http.Put)
+    |> request.set_header("content-type", "application/json")
+    |> request.set_header("authorization", basic_auth(
+      config.admin_user,
+      config.admin_password,
+    ))
+    |> request.set_body(doc)
+  case httpc.send(req) {
+    Error(_) -> error_json(502, "couchdb_unreachable")
+    Ok(resp) ->
+      case resp.status {
+        201 | 202 ->
+          json_response(
+            201,
+            json.object([
+              #("ok", json.bool(True)),
+              #("username", json.string(username)),
+            ]),
+          )
+        409 -> error_json(409, "user_exists")
+        401 | 403 -> error_json(500, "admin_auth_failed")
+        _ -> error_json(502, "couchdb_error")
+      }
+  }
+}
+
+fn basic_auth(user: String, password: String) -> String {
+  let creds = user <> ":" <> password
+  "Basic " <> bit_array.base64_encode(<<creds:utf8>>, True)
+}
+
+fn error_json(status: Int, code: String) -> Response {
+  json_response(status, json.object([#("error", json.string(code))]))
+}
+
+fn json_response(status: Int, body: json.Json) -> Response {
+  wisp.json_response(json.to_string_tree(body), status)
+}