add startFaceLivenessSession spi (#136)

Author: atierian

AmplifyPlugins/Predictions/AWSPredictionsPlugin/Liveness/SPI/AWSPredictionsPlugin+Liveness.swift

@@ -0,0 +1,61 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+import Foundation
+import Amplify
+import AWSPluginsCore
+
+extension AWSPredictionsPlugin {
+    @_spi(PredictionsFaceLiveness)
+    public static func startFaceLivenessSession(
+        withID sessionID: String,
+        credentialsProvider: AWSCredentialsProvider? = nil,
+        region: String,
+        options: FaceLivenessSession.Options,
+        completion: @escaping (Result<Void, FaceLivenessSessionError>) -> Void
+    ) async throws -> FaceLivenessSession {
+
+        let credential = try await credential(from: credentialsProvider)
+
+        let signer = SigV4Signer(
+            credential: .init(
+                accessKey: credential.accessKey,
+                secretKey: credential.secretKey,
+                sessionToken: credential.sessionToken
+            ),
+            serviceName: "rekognition",
+            region: region
+        )
+
+        let url = try streamingSessionURL(for: region)
+
+        let session = FaceLivenessSession(
+            websocket: WebSocketSession(),
+            signer: signer,
+            baseURL: url
+        )
+
+        return session
+    }
+}
+
+extension FaceLivenessSession {
+    @_spi(PredictionsFaceLiveness)
+    public struct Options {
+        public init() {}
+    }
+}
+
+@_spi(PredictionsFaceLiveness)
+public struct FaceLivenessSessionError: Swift.Error, Equatable {
+    public let code: UInt8
+
+    public static let accessDenied = Self(code: 0)
+    public static let invalidRegion = Self(code: 1)
+    public static let invalidURL = Self(code: 2)
+}
+

AmplifyPlugins/Predictions/AWSPredictionsPlugin/Liveness/SPI/LivenessCredentials.swift

@@ -0,0 +1,37 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+import Foundation
+import Amplify
+import AWSPluginsCore
+
+func credential(from credentialsProvider: AWSCredentialsProvider?) async throws -> SigV4Signer.Credential {
+    let credential: SigV4Signer.Credential
+
+    if let credentialsProvider = credentialsProvider {
+        let providedCredentials = try await credentialsProvider.fetchAWSCredentials()
+        credential = .init(
+            accessKey: providedCredentials.accessKeyId,
+            secretKey: providedCredentials.secretAccessKey,
+            sessionToken: (providedCredentials as? AWSTemporaryCredentials)?.sessionToken
+        )
+    } else {
+        let authSession = try await Amplify.Auth.fetchAuthSession()
+        if let authAWSCredentialsProvider = authSession as? AuthAWSCredentialsProvider {
+            let awsCredentials = try authAWSCredentialsProvider.getAWSCredentials().get()
+            credential = .init(
+                accessKey: awsCredentials.accessKeyId,
+                secretKey: awsCredentials.secretAccessKey,
+                sessionToken: (awsCredentials as? AWSTemporaryCredentials)?.sessionToken
+            )
+        } else {
+            throw FaceLivenessSessionError.accessDenied
+        }
+    }
+
+    return credential
+}

AmplifyPlugins/Predictions/AWSPredictionsPlugin/Liveness/SPI/LivenessStreamingURL.swift

@@ -0,0 +1,16 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+import Foundation
+
+func streamingSessionURL(for region: String) throws -> URL {
+    let urlString = "wss://streaming-rekognition.\(region).amazonaws.com/start-face-liveness-session-websocket"
+    guard let url = URL(string: urlString) else {
+        throw FaceLivenessSessionError.invalidRegion
+    }
+    return url
+}