Add PresentationExchange.selectCredentials

Package.swift

@@ -21,6 +21,8 @@ let package = Package(
         .package(url: "https://github.com/allegro/swift-junit.git", from: "2.1.0"),
         .package(url: "https://github.com/flight-school/anycodable.git", from: "0.6.7"),
         .package(url: "https://github.com/Bouke/DNS.git", from: "1.2.0"),
+        .package(url: "https://github.com/KittyMac/Sextant.git", exact: "0.4.0"),
+        .package(url: "https://github.com/kylef/JSONSchema.swift.git", from: "0.6.0")
     ],
     targets: [
         .target(
@@ -30,6 +32,8 @@ let package = Package(
                 .product(name: "ExtrasBase64", package: "swift-extras-base64"),
                 .product(name: "AnyCodable", package: "anycodable"),
                 .product(name: "DNS", package: "DNS"),
+                .product(name: "Sextant", package: "sextant"),
+                .product(name: "JSONSchema", package: "jsonschema.swift")
             ]
         ),
         .testTarget(

Sources/Web5/Common/FlatMap.swift

@@ -0,0 +1,29 @@
+import AnyCodable
+import Foundation
+
+/// Wrapper used to easily encode a `[String: AnyCodable]` to and decode a `[String: AnyCodable]` from a flat map.
+@propertyWrapper
+struct FlatMap: Codable {
+    var wrappedValue: [String: AnyCodable]?
+
+    init(wrappedValue: [String: AnyCodable]?) {
+        self.wrappedValue = wrappedValue
+    }
+
+    init(from decoder: Decoder) throws {
+        let value = try decoder.singleValueContainer()
+        if let mapValue = try? value.decode([String: AnyCodable].self) {
+            wrappedValue = mapValue
+        } else {
+            throw DecodingError.typeMismatch(Date.self, DecodingError.Context(codingPath: [], debugDescription: "TODO"))
+        }
+    }
+
+    func encode(to encoder: Encoder) throws {
+        var container = encoder.singleValueContainer()
+
+        if let wrappedValue {
+            try container.encode(wrappedValue)
+        }
+    }
+}

Sources/Web5/Common/ISO8601Date.swift

@@ -1,3 +1,4 @@
+import AnyCodable
 import Foundation
 
 /// Wrapper used to easily encode a `Date` to and decode a `Date` from an ISO 8601 formatted date string.

Sources/Web5/Common/OneOrMany.swift

@@ -33,6 +33,13 @@ public enum OneOrMany<T: Codable & Equatable>: Codable, Equatable {
             return nil
         }
     }
+    /*
+     {
+      thing: "thing",
+     "grab": {
+     "thing" : "thing"
+     }
+     */
 
     public init(from decoder: Decoder) throws {
         let container = try decoder.singleValueContainer()

Sources/Web5/Credentials/PresentationExchange.swift

@@ -0,0 +1,220 @@
+import AnyCodable
+import Foundation
+import Sextant
+import JSONSchema
+
+public struct VCDataModel: Codable {
+    public let context: [String]
+    public let id: String
+    public let type: [String]
+    public let issuer: String
+    public let issuanceDate: String
+    public let expirationDate: String?
+    public let credentialSubject: [String: AnyCodable]
+    public let credentialStatus: CredentialStatus?
+    public let credentialSchema: CredentialSchema?
+    public let evidence: [String: AnyCodable]?
+
+    enum CodingKeys: String, CodingKey {
+        case context = "@context"
+        case id
+        case type
+        case issuer
+        case issuanceDate
+        case expirationDate
+        case credentialSubject
+        case credentialStatus
+        case credentialSchema
+        case evidence
+    }
+}
+
+public struct CredentialStatus: Codable {
+    public let id: String
+    public let type: String
+    public let statusPurpose: String
+    public let statusListIndex: String
+    public let statusListCredential: String
+}
+
+public struct CredentialSchema: Codable {
+    public let id: String
+    public let type: String
+}
+
+public struct PresentationDefinitionV2: Codable {
+    public let inputDescriptors: [InputDescriptorV2]
+}
+
+public struct InputDescriptorV2: Codable, Hashable {
+    public let constraints: ConstraintsV2
+}
+
+public struct ConstraintsV2: Codable, Hashable {
+    public let fields: [FieldV2]?
+}
+
+public struct FieldV2: Codable, Hashable {
+    public let id: String?
+    public let path: [String]
+    public let purpose: String?
+    public let filter: [String: AnyCodable]?
+    public let predicate: Optionality?
+    public let name: String?
+    public let optional: Bool?
+
+    public init(
+        id: String? = nil,
+        path: [String],
+        purpose: String? = nil,
+        filter: [String: AnyCodable]? = nil,
+        predicate: Optionality? = nil,
+        name: String? = nil,
+        optional: Bool? = nil
+    ) {
+        self.id = id
+        self.path = path
+        self.purpose = purpose
+        self.filter = filter
+        self.predicate = predicate
+        self.name = name
+        self.optional = optional
+    }
+}
+
+public enum Optionality: Codable {
+    case required
+    case preferred
+}
+
+public enum PresentationExchange {
+
+    // MARK: - Select Credentials
+    public static func selectCredentials(
+        vcJWTs: [String],
+        presentationDefinition: PresentationDefinitionV2
+    ) throws -> [String] {
+        let inputDescriptorToVcMap = try mapInputDescriptorsToVCs(vcJWTList: vcJWTs, presentationDefinition: presentationDefinition)
+        return inputDescriptorToVcMap.flatMap { $0.value }
+    }
+
+    // MARK: - Satisfies Presentation Definition
+    public static func satisfiesPresentationDefinition(
+        vcJWTs: [String],
+        presentationDefinition: PresentationDefinitionV2
+    ) throws -> Void {
+        let inputDescriptorToVcMap = try selectCredentials(vcJWTs: vcJWTs, presentationDefinition: presentationDefinition)
+        guard inputDescriptorToVcMap.count == presentationDefinition.inputDescriptors.count else {
+            print("this is testing it reaches this line")
+            throw Error.missingCredentials(presentationDefinition.inputDescriptors.count, inputDescriptorToVcMap.count)
+        }
+    }
+
+    // MARK: - Map Input Descriptors to VCs
+    private static func mapInputDescriptorsToVCs(
+        vcJWTList: [String],
+        presentationDefinition: PresentationDefinitionV2
+    ) throws -> [InputDescriptorV2: [String]] {
+        let vcJWTListMap: [VCDataModel] = try vcJWTList.map { vcJWT in
+                let parsedJWT  = try JWT.parse(jwtString: vcJWT)
+                guard let vcJSON = parsedJWT.payload["vc"]?.value as? [String: Any] else {
+                    throw Error.missingCredentialObject
+                }
+
+                let vcData = try JSONSerialization.data(withJSONObject: vcJSON)
+                let vc = try JSONDecoder().decode(VCDataModel.self, from: vcData)
+
+                return vc
+            }
+
+        let vcJwtListWithNodes = zip(vcJWTList, vcJWTListMap)
+
+        let result = try presentationDefinition.inputDescriptors.reduce(into: [InputDescriptorV2: [String]]()) { result, inputDescriptor in
+            let vcJwtList = try vcJwtListWithNodes.filter { (_, node) in
+                try vcSatisfiesInputDescriptor(vc: node, inputDescriptor: inputDescriptor)
+            }.map { (vcJwt, _) in
+                vcJwt
+            }
+            if !vcJwtList.isEmpty {
+                result[inputDescriptor] = vcJwtList
+            }
+        }
+        return result
+    }
+
+    // MARK: - VC Satisfies Input Descriptor
+    private static func vcSatisfiesInputDescriptor(vc: VCDataModel, inputDescriptor: InputDescriptorV2) throws -> Bool {
+        // If the Input Descriptor has constraints and fields defined, evaluate them.
+        guard let fields = inputDescriptor.constraints.fields else {
+            // If no fields are defined, VC satisfies
+            return true
+        }
+
+        let requiredFields = fields.filter { !($0.optional ?? false) }
+
+        for field in requiredFields {
+
+            // Takes field.path and queries the vc to see if there is a corresponding path.
+            let vcJson = try JSONEncoder().encode(vc)
+            guard let matchedPathValues = vcJson.query(values: field.path) else { return false }
+
+
+            if matchedPathValues.isEmpty {
+                // If no matching fields are found for a required field, the VC does not satisfy this Input Descriptor.
+                return false
+            }
+
+            // If there is a filter, process it
+            if let filter = field.filter {
+                let fieldName = field.path[0]
+
+                var filterProperties: [String: [String: String]] = [:]
+
+                for (filterKey, filterValue) in filter {
+                    guard let filterRule = filterValue.value as? String else {
+                        return false
+                    }
+
+                    filterProperties[fieldName, default: [:]][filterKey] = filterRule
+                }
+
+                let satisfiesSchemaMatches = try matchedPathValues.filter { value in
+                    let result = try JSONSchema.validate([fieldName: value], schema: [
+                      "properties": filterProperties
+                    ])
+                    return result.valid
+                }
+
+                if satisfiesSchemaMatches.isEmpty {
+                    // If the field value does not satisfy the schema, the VC does not satisfy this Input Descriptor.
+                    return false
+                }
+            }
+        }
+
+        // If the VC passes all the checks, it satisfies the criteria of the Input Descriptor.
+        return true
+    }
+
+}
+
+// MARK: - Errors
+extension PresentationExchange {
+    public enum Error: LocalizedError {
+        case missingCredentialObject
+        case missingCredentials(Int, Int)
+
+        public var errorDescription: String? {
+            switch self {
+            case .missingCredentialObject:
+                return "Failed to find Verifiable Credential object in parsed JWT"
+            case .missingCredentials(let totalNeeded, let actualReceived):
+                return """
+                Missing input descriptors: The presentation definition requires
+                \(totalNeeded) descriptors, but only
+                \(actualReceived) were found. Check and provide the missing descriptors.
+                """
+            }
+        }
+    }
+}

Sources/Web5/Crypto/JOSE/JWT.swift

@@ -1,4 +1,5 @@
 import Foundation
+import AnyCodable
 
 public struct JWT {
 
@@ -90,4 +91,64 @@ public struct JWT {
             )
         )
     }
+
+    public struct ParsedJWT {
+        let header: JWS.Header
+        let payload: [String: AnyCodable]
+
+        public init(
+            header: JWS.Header,
+            payload: [String: AnyCodable]
+        ) {
+            self.header = header
+            self.payload = payload
+        }
+    }
+
+    public static func parse(jwtString: String) throws -> ParsedJWT {
+        let parts = jwtString.components(separatedBy: ".")
+
+        guard parts.count == 3 else {
+            throw Error.verificationFailed("Malformed JWT. Expected 3 parts. Got \(parts.count)")
+        }
+
+        let base64urlEncodedJwtHeader = String(parts[0])
+        let base64urlEncodedJwtPayload = String(parts[1])
+        let _ = String(parts[2])
+
+        let jwtHeader: JWS.Header = try JSONDecoder().decode(
+            JWS.Header.self,
+            from: try base64urlEncodedJwtHeader.decodeBase64Url()
+        )
+
+        guard jwtHeader.type == "JWT" else {
+            throw Error.verificationFailed("Expected JWT header to contain typ property set to JWT")
+        }
+
+        guard let _ = jwtHeader.keyID else {
+            throw Error.verificationFailed("Expected JWT header to contain kid")
+        }
+
+        let jwtPayload = try JSONDecoder().decode(
+            [String: AnyCodable].self,
+            from: base64urlEncodedJwtPayload.decodeBase64Url()
+        )
+
+        return ParsedJWT(header: jwtHeader, payload: jwtPayload)
+    }
+}
+
+// MARK: - Errors
+
+extension JWT {
+    public enum Error: LocalizedError {
+        case verificationFailed(String)
+
+        public var errorDescription: String? {
+            switch self {
+            case let .verificationFailed(reason):
+                return "Verification Failed: \(reason)"
+            }
+        }
+    }
 }