Support plaintext auths from Docker config (#219)

Sources/tart/Credentials/DockerConfigCredentialsProvider.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-class HelperProgramCredentialsProvider: CredentialsProvider {
+class DockerConfigCredentialsProvider: CredentialsProvider {
   func retrieve(host: String) throws -> (String, String)? {
     let dockerConfigURL = FileManager.default.homeDirectoryForCurrentUser.appendingPathComponent(".docker").appendingPathComponent("config.json")
     if !FileManager.default.fileExists(atPath: dockerConfigURL.path) {
@@ -8,6 +8,9 @@ class HelperProgramCredentialsProvider: CredentialsProvider {
     }
     let config = try JSONDecoder().decode(DockerConfig.self, from: Data(contentsOf: dockerConfigURL))
 
+    if let credentialsFromAuth = config.auths?[host]?.decodeCredentials() {
+      return credentialsFromAuth
+    }
     if let helperProgram = config.credHelpers?[host] {
       return try executeHelper(binaryName: "docker-credential-\(helperProgram)", host: host)
     }
@@ -54,9 +57,31 @@ class HelperProgramCredentialsProvider: CredentialsProvider {
 }
 
 struct DockerConfig: Codable {
+  var auths: Dictionary<String, DockerAuthConfig>? = Dictionary()
   var credHelpers: Dictionary<String, String>? = Dictionary()
 }
 
+struct DockerAuthConfig: Codable {
+  var auth: String? = nil
+
+  func decodeCredentials() -> (String, String)? {
+    // auth is a base64("username:password")
+    guard let authBase64 = auth else {
+      return nil
+    }
+    guard let data = Data(base64Encoded: authBase64) else {
+      return nil
+    }
+    guard let components = String(data: data, encoding: .utf8)?.components(separatedBy: ":") else {
+      return nil
+    }
+    if components.count != 2 {
+      return nil
+    }
+    return (components[0], components[1])
+  }
+}
+
 struct DockerGetOutput: Codable {
   var Username: String
   var Secret: String

Sources/tart/OCI/Registry.swift

@@ -94,7 +94,7 @@ class Registry {
 
   init(urlComponents: URLComponents,
        namespace: String,
-       credentialsProviders: [CredentialsProvider] = [HelperProgramCredentialsProvider(), KeychainCredentialsProvider()]
+       credentialsProviders: [CredentialsProvider] = [DockerConfigCredentialsProvider(), KeychainCredentialsProvider()]
   ) throws {
     baseURL = urlComponents.url!
     self.namespace = namespace
@@ -105,7 +105,7 @@ class Registry {
     host: String,
     namespace: String,
     insecure: Bool = false,
-    credentialsProviders: [CredentialsProvider] = [HelperProgramCredentialsProvider(), KeychainCredentialsProvider()]
+    credentialsProviders: [CredentialsProvider] = [DockerConfigCredentialsProvider(), KeychainCredentialsProvider()]
   ) throws {
     let proto = insecure ? "http" : "https"
     let baseURLComponents = URLComponents(string: proto + "://" + host + "/v2/")!