Polish up Passkey interface

- Fix indentation
- Split awkward initializer into separate methods
- Rename credentials to passkeys
- Simplify authenticator registry loading
- Flatten nested errors under ActionPack::WebAuthn
- Set passkey current params only requests that use it
- Inline anemic methods
- Replace custom validation with ActiveModel::Validation
- Rename identity to holder in Passkey
- Rename credentials to passkeys in JS
- Extract framework library out of controllers
- Pass params hashes down to ActionPack
- Attempt to simplify public interface
- Push data decoding down to the classes representing the data
- Introduce has_passkeys
- Add CBOR bigint support
- Rename ActionPack::WebAuthn::Passkey to ActionPack::Passkey
- Add create_passkey_button helper
- Rename public-key to creation-options
- Add sign_in_with_passkey_button helper
- Dispatch events for the whole Passkey lifecycle
- Add ED25519 support
- Prevent crash on missing meta tag
- Validate resident key options
- Don't clobber existing ActionPack config options
- Validate cryptographic params
- Move CurrentWebAuthnRequest into ActionPack::Passkey
- Use ActiveModel::Attributes for Options objects
- Implement expiring challanges
- Add lifecycle events
- Extract param helpers into Request
- Add passkey_creation_options and passkey_request_options helpers
- Add create_passkey_challenge to make it easier to override the create method if needed
- Prefix all view helpers with passkey_
- Auto-include ActionPack::Passkey::Holder
- Make the passkey challange url configurable
- Add a reminder about Passkeys to the magic link email

lib/action_pack/web_authn/cose_key.rb

@@ -19,22 +19,25 @@
 # [ES256]
 #   ECDSA with P-256 curve and SHA-256. The most common algorithm for WebAuthn.
 #
+# [EdDSA]
+#   EdDSA with Ed25519 curve. Increasingly supported by modern authenticators.
+#
 # [RS256]
 #   RSASSA-PKCS1-v1_5 with SHA-256. Used by some security keys and platforms.
 #
 # == Attributes
 #
 # [+key_type+]
-#   The COSE key type (2 for EC2, 3 for RSA).
+#   The COSE key type (1 for OKP, 2 for EC2, 3 for RSA).
 #
 # [+algorithm+]
-#   The COSE algorithm identifier (-7 for ES256, -257 for RS256).
+#   The COSE algorithm identifier (-7 for ES256, -8 for EdDSA, -257 for RS256).
 #
 # [+parameters+]
 #   The full COSE key parameters map, including curve and coordinate data.
 class ActionPack::WebAuthn::CoseKey
-  # Raised when the key type, algorithm, or curve is not supported.
-  class UnsupportedKeyTypeError < StandardError; end
+  P256_COORDINATE_LENGTH = 32
+  MINIMUM_RSA_KEY_BITS = 2048
 
   # COSE key labels
   KEY_TYPE_LABEL = 1
@@ -44,18 +47,25 @@ class ActionPack::WebAuthn::CoseKey
   EC2_Y_LABEL = -3
   RSA_N_LABEL = -1
   RSA_E_LABEL = -2
+  OKP_CURVE_LABEL = -1
+  OKP_X_LABEL = -2
 
   # COSE key types
+  OKP = 1
   EC2 = 2
   RSA = 3
 
   # COSE algorithms
   ES256 = -7
+  EDDSA = -8
   RS256 = -257
 
   # COSE EC2 curves
   P256 = 1
 
+  # COSE OKP curves
+  ED25519 = 6
+
   # OpenSSL types
   UNCOMPRESSED_POINT_MARKER = 0x04
 
@@ -84,26 +94,30 @@ class ActionPack::WebAuthn::CoseKey
 
   # Converts the COSE key to an OpenSSL public key object.
   #
-  # Returns an +OpenSSL::PKey::EC+ for EC2 keys or +OpenSSL::PKey::RSA+ for
-  # RSA keys, suitable for use with +OpenSSL::PKey#verify+.
+  # Returns an +OpenSSL::PKey::EC+ for EC2 keys, +OpenSSL::PKey::RSA+ for
+  # RSA keys, or an Ed25519 key for OKP keys, suitable for use with
+  # +OpenSSL::PKey#verify+.
   #
   # Raises +UnsupportedKeyTypeError+ if the key type, algorithm, or curve
   # is not supported.
   def to_openssl_key
     case [ key_type, algorithm ]
     when [ EC2, ES256 ] then build_ec2_es256_key
+    when [ OKP, EDDSA ] then build_okp_eddsa_key
     when [ RSA, RS256 ] then build_rsa_rs256_key
-    else raise UnsupportedKeyTypeError, "Unsupported COSE key type/algorithm: #{key_type}/#{algorithm}"
+    else raise ActionPack::WebAuthn::UnsupportedKeyTypeError, "Unsupported COSE key type/algorithm: #{key_type}/#{algorithm}"
     end
   end
 
   private
     def build_ec2_es256_key
       curve = parameters[EC2_CURVE_LABEL]
-      raise UnsupportedKeyTypeError, "Unsupported EC curve: #{curve}" unless curve == P256
+      raise ActionPack::WebAuthn::UnsupportedKeyTypeError, "Unsupported EC curve: #{curve}" unless curve == P256
 
       x = parameters[EC2_X_LABEL]
       y = parameters[EC2_Y_LABEL]
+      raise ActionPack::WebAuthn::InvalidKeyError, "Missing EC2 key coordinates" if x.nil? || y.nil?
+      raise ActionPack::WebAuthn::InvalidKeyError, "Invalid EC2 coordinate length" unless x.bytesize == P256_COORDINATE_LENGTH && y.bytesize == P256_COORDINATE_LENGTH
 
       # Uncompressed point format: 0x04 || x || y
       public_key_bytes = [ UNCOMPRESSED_POINT_MARKER, *x.bytes, *y.bytes ].pack("C*")
@@ -117,11 +131,37 @@ class ActionPack::WebAuthn::CoseKey
       ])
 
       OpenSSL::PKey::EC.new(asn1.to_der)
+    rescue OpenSSL::PKey::PKeyError => error
+      raise ActionPack::WebAuthn::InvalidKeyError, "Invalid EC2 key: #{error.message}"
+    end
+
+    def build_okp_eddsa_key
+      curve = parameters[OKP_CURVE_LABEL]
+      raise ActionPack::WebAuthn::UnsupportedKeyTypeError, "Unsupported OKP curve: #{curve}" unless curve == ED25519
+
+      x = parameters[OKP_X_LABEL]
+      raise ActionPack::WebAuthn::InvalidKeyError, "Missing OKP key coordinate" if x.nil?
+
+      asn1 = OpenSSL::ASN1::Sequence([
+        OpenSSL::ASN1::Sequence([
+          OpenSSL::ASN1::ObjectId("ED25519")
+        ]),
+        OpenSSL::ASN1::BitString(x)
+      ])
+
+      OpenSSL::PKey.read(asn1.to_der)
+    rescue OpenSSL::PKey::PKeyError => error
+      raise ActionPack::WebAuthn::InvalidKeyError, "Invalid OKP key: #{error.message}"
     end
 
     def build_rsa_rs256_key
-      n = OpenSSL::BN.new(parameters[RSA_N_LABEL], 2)
-      e = OpenSSL::BN.new(parameters[RSA_E_LABEL], 2)
+      n_bytes = parameters[RSA_N_LABEL]
+      e_bytes = parameters[RSA_E_LABEL]
+      raise ActionPack::WebAuthn::InvalidKeyError, "Missing RSA key parameters" if n_bytes.nil? || e_bytes.nil?
+      raise ActionPack::WebAuthn::InvalidKeyError, "RSA key must be at least #{MINIMUM_RSA_KEY_BITS} bits" if n_bytes.bytesize * 8 < MINIMUM_RSA_KEY_BITS
+
+      n = OpenSSL::BN.new(n_bytes, 2)
+      e = OpenSSL::BN.new(e_bytes, 2)
 
       asn1 = OpenSSL::ASN1::Sequence([
         OpenSSL::ASN1::Sequence([
@@ -137,5 +177,7 @@ class ActionPack::WebAuthn::CoseKey
       ])
 
       OpenSSL::PKey::RSA.new(asn1.to_der)
+    rescue OpenSSL::PKey::PKeyError => error
+      raise ActionPack::WebAuthn::InvalidKeyError, "Invalid RSA key: #{error.message}"
     end
 end