Module: Mistri::MCP::OAuth

Defined in:
lib/mistri/mcp/oauth.rb

Overview

The OAuth 2.1 subset the MCP spec requires of clients, as three storage-agnostic services a host calls from anywhere: a controller, a GraphQL mutation, a job. Each returns a string-keyed hash ready to persist on the host's own connection record.

flow = Mistri::MCP::OAuth.start(url: params[:url],
                              client_name: "Sendoso",
                              redirect_uri: mcp_callback_url)
# persist flow, redirect the user to flow["authorize_url"]

tokens = Mistri::MCP::OAuth.complete(code: params[:code], **persisted)
tokens = Mistri::MCP::OAuth.refresh(**persisted)

Registration happens as the APPLICATION, never as the harness: client_name has no default because that identity is the host's call. Servers without dynamic registration take client_id:/client_secret: directly and skip it.

Class Method Summary collapse

Class Method Details

.authorize_url(metadata, grant) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 191

def authorize_url(metadata, grant)
  challenge = Digest::SHA256.base64digest(grant[:verifier]).tr("+/", "-_").delete("=")
  params = { "response_type" => "code", "client_id" => grant[:client_id],
             "redirect_uri" => grant[:redirect_uri], "state" => grant[:state],
             "code_challenge" => challenge, "code_challenge_method" => "S256",
             "resource" => grant[:resource] }
  params["scope"] = grant[:scope] if grant[:scope]
  endpoint = URI(metadata.fetch("authorization_endpoint"))
  endpoint.query = [endpoint.query, URI.encode_www_form(params)].compact.join("&")
  endpoint.to_s
end

.canonical(url) ⇒ Object

RFC 8707 canonical form: lowercase scheme and host, no fragment.



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# File 'lib/mistri/mcp/oauth.rb', line 206

def canonical(url)
  uri = URI(url)
  uri.fragment = nil
  uri.scheme = uri.scheme.downcase
  uri.host = uri.host.downcase if uri.host
  uri.to_s
end

.challenge_metadata_url(url) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 96

def challenge_metadata_url(url)
  uri = URI(url)
  response = http(uri) do |connection|
    request = Net::HTTP::Post.new(uri)
    request["Accept"] = "application/json, text/event-stream"
    request["Content-Type"] = "application/json"
    request.body = JSON.generate({ jsonrpc: "2.0", id: 0, method: "ping" })
    connection.request(request)
  end
  challenge = response["WWW-Authenticate"].to_s
  challenge[/resource_metadata="([^"]+)"/i, 1]
end

.complete(code:, code_verifier:, client_id:, token_endpoint:, resource:, redirect_uri:, client_secret: nil, token_auth_method: nil) ⇒ Object

Exchange the callback's code for tokens.



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# File 'lib/mistri/mcp/oauth.rb', line 65

def complete(code:, code_verifier:, client_id:, token_endpoint:, resource:,
             redirect_uri:, client_secret: nil, token_auth_method: nil, **)
  form = { "grant_type" => "authorization_code", "code" => code,
           "code_verifier" => code_verifier, "client_id" => client_id,
           "redirect_uri" => redirect_uri, "resource" => resource }
  token_request(token_endpoint, form, client_secret, token_auth_method)
end

.get_json(url) ⇒ Object

Raises:



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# File 'lib/mistri/mcp/oauth.rb', line 228

def get_json(url)
  uri = URI(url)
  response = http(uri) { |connection| connection.request(Net::HTTP::Get.new(uri)) }
  raise Error, "GET #{url} answered #{response.code}" unless response.code.to_i == 200

  JSON.parse(response.body)
end

.http(uri) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 280

def http(uri, &)
  Net::HTTP.start(uri.host, uri.port, use_ssl: uri.scheme == "https",
                                      open_timeout: 15, read_timeout: 30, &)
end

.post_form(url, form, basic_auth: nil) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 257

def post_form(url, form, basic_auth: nil)
  uri = URI(url)
  response = http(uri) do |connection|
    request = Net::HTTP::Post.new(uri)
    request["Content-Type"] = "application/x-www-form-urlencoded"
    request["Accept"] = "application/json"
    request.basic_auth(*basic_auth) if basic_auth
    request.body = URI.encode_www_form(form)
    connection.request(request)
  end
  payload = begin
    JSON.parse(response.body)
  rescue StandardError
    {}
  end
  unless response.code.to_i == 200
    reason = payload["error_description"] || payload["error"] || response.body.to_s[0, 200]
    raise Error, "token request failed (#{response.code}): #{reason}"
  end

  payload
end

.post_json(url, body) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 242

def post_json(url, body)
  uri = URI(url)
  response = http(uri) do |connection|
    request = Net::HTTP::Post.new(uri)
    request["Content-Type"] = "application/json"
    request.body = JSON.generate(body)
    connection.request(request)
  end
  unless %w[200 201].include?(response.code)
    raise Error, "POST #{url} answered #{response.code}: #{response.body.to_s[0, 200]}"
  end

  JSON.parse(response.body)
end

.presence(value) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 187

def presence(value)
  value.to_s.strip.empty? ? nil : value
end

.refresh(refresh_token:, client_id:, token_endpoint:, resource:, client_secret: nil, token_auth_method: nil) ⇒ Object

Trade a refresh token for a fresh set; OAuth 2.1 rotates refresh tokens, so persist the returned one.



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# File 'lib/mistri/mcp/oauth.rb', line 75

def refresh(refresh_token:, client_id:, token_endpoint:, resource:,
            client_secret: nil, token_auth_method: nil, **)
  form = { "grant_type" => "refresh_token", "refresh_token" => refresh_token,
           "client_id" => client_id, "resource" => resource }
  token_request(token_endpoint, form, client_secret, token_auth_method)
end

.register(metadata, client_name, redirect_uri, client_id, client_secret) ⇒ Object

RFC 7591 dynamic registration, as the application. Servers without a registration endpoint require a pre-registered client id. The returned hash keeps the token endpoint auth method the server granted, so token requests authenticate the way it expects.



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# File 'lib/mistri/mcp/oauth.rb', line 135

def register(metadata, client_name, redirect_uri, client_id, client_secret)
  return { "client_id" => client_id, "client_secret" => client_secret } if client_id

  endpoint = metadata["registration_endpoint"]
  unless endpoint
    raise Error, "the server does not offer dynamic client registration; " \
                 "pass client_id:/client_secret: from a manual registration"
  end

  registration = post_json(endpoint, {
                             "client_name" => client_name,
                             "redirect_uris" => [redirect_uri],
                             "grant_types" => %w[authorization_code refresh_token],
                             "response_types" => ["code"],
                             "token_endpoint_auth_method" => "client_secret_post"
                           })
  {
    "client_id" => presence(registration["client_id"]) ||
      raise(Error, "registration returned no client_id"),
    "client_secret" => presence(registration["client_secret"]),
    "token_endpoint_auth_method" => presence(registration["token_endpoint_auth_method"])
  }
end

.resolve_scope(scope, resource_metadata, metadata) ⇒ Object

No scope given: request what the resource advertises, and add offline_access when the authorization server supports it (that is what earns a refresh token from providers that require it). An unsupported offline_access is stripped rather than sent blind.



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# File 'lib/mistri/mcp/oauth.rb', line 163

def resolve_scope(scope, resource_metadata, metadata)
  scopes = scope.to_s.split
  scopes = Array(resource_metadata["scopes_supported"]) if scopes.empty?
  supported = Array(metadata["scopes_supported"])
  if supported.include?("offline_access")
    scopes |= ["offline_access"]
  else
    scopes -= ["offline_access"]
  end
  scopes.empty? ? nil : scopes.join(" ")
end

.resource_metadata_for(url) ⇒ Object

RFC 9728: a 401's WWW-Authenticate names the resource metadata URL; servers that skip the header serve the well-known path.



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# File 'lib/mistri/mcp/oauth.rb', line 86

def resource_metadata_for(url)
  metadata_url = challenge_metadata_url(url) || well_known_resource_url(url)
  document = get_json(metadata_url)
  if Array(document["authorization_servers"]).empty?
    raise Error, "#{metadata_url} names no authorization servers"
  end

  document
end

.server_metadata(authority) ⇒ Object

RFC 8414 metadata, with the OpenID Connect path as a fallback since large providers often serve only that document.

Raises:



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# File 'lib/mistri/mcp/oauth.rb', line 118

def server_metadata(authority)
  uri = URI(authority)
  origin = "#{uri.scheme}://#{uri.host}:#{uri.port}"
  path = uri.path.chomp("/")
  candidates = ["#{origin}/.well-known/oauth-authorization-server#{path unless path.empty?}",
                "#{origin}#{path}/.well-known/openid-configuration"]
  candidates.each do |candidate|
    document = try_json(candidate)
    return document if document&.key?("token_endpoint")
  end
  raise Error, "no authorization server metadata at #{authority}"
end

.start(url:, client_name:, redirect_uri:, scope: nil, client_id: nil, client_secret: nil) ⇒ Object

Discover the server's authorization setup, register the application, and build the authorize URL. Returns everything the callback and refresh need: authorize_url, state, code_verifier, client_id, client_secret, token_auth_method, token_endpoint, resource, redirect_uri.

With no scope given, the server's advertised scopes_supported are requested, and offline_access rides along when the authorization server supports it, which is what earns a refresh token from providers that require it.



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# File 'lib/mistri/mcp/oauth.rb', line 41

def start(url:, client_name:, redirect_uri:, scope: nil,
          client_id: nil, client_secret: nil)
  resource = canonical(url)
  resource_metadata = resource_metadata_for(url)
  metadata = server_metadata(Array(resource_metadata["authorization_servers"]).first)
  validate_endpoints(metadata)
  registration = register(metadata, client_name, redirect_uri, client_id, client_secret)
  verifier = SecureRandom.urlsafe_base64(48)
  state = SecureRandom.urlsafe_base64(32)
  grant = { client_id: registration["client_id"], redirect_uri: redirect_uri,
            verifier: verifier, state: state, resource: resource,
            scope: resolve_scope(scope, resource_metadata, metadata) }
  {
    "authorize_url" => authorize_url(metadata, grant),
    "state" => state, "code_verifier" => verifier,
    "client_id" => registration["client_id"],
    "client_secret" => registration["client_secret"],
    "token_auth_method" => registration["token_endpoint_auth_method"],
    "token_endpoint" => metadata.fetch("token_endpoint"),
    "resource" => resource, "redirect_uri" => redirect_uri
  }
end

.token_request(endpoint, form, client_secret, auth_method = nil) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 214

def token_request(endpoint, form, client_secret, auth_method = nil)
  basic = client_secret && auth_method == "client_secret_basic"
  form = form.merge("client_secret" => client_secret) if client_secret && !basic
  credentials = basic ? [form["client_id"], client_secret] : nil
  payload = post_form(endpoint, form, basic_auth: credentials)
  expires_in = payload["expires_in"]
  {
    "access_token" => payload.fetch("access_token"),
    "refresh_token" => payload["refresh_token"],
    "scope" => payload["scope"],
    "expires_at" => expires_in ? Time.now.utc + expires_in.to_i : nil
  }
end

.try_json(url) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 236

def try_json(url)
  get_json(url)
rescue Error, JSON::ParserError
  nil
end

.validate_endpoints(metadata) ⇒ Object

The spec requires authorization server endpoints over HTTPS; loopback stays allowed for development.



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# File 'lib/mistri/mcp/oauth.rb', line 177

def validate_endpoints(metadata)
  %w[authorization_endpoint token_endpoint registration_endpoint].each do |key|
    value = metadata[key] or next
    uri = URI(value)
    next if uri.scheme == "https" || %w[localhost 127.0.0.1 ::1].include?(uri.host)

    raise Error, "#{key} #{value} is not HTTPS"
  end
end

.well_known_resource_url(url) ⇒ Object 



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# File 'lib/mistri/mcp/oauth.rb', line 109

def well_known_resource_url(url)
  uri = URI(url)
  path = uri.path.chomp("/")
  origin = "#{uri.scheme}://#{uri.host}:#{uri.port}"
  "#{origin}/.well-known/oauth-protected-resource#{path unless path.empty?}"
end