diff --git a/Sources/CryptomatorCloudAccess/Box/BoxCloudProvider.swift b/Sources/CryptomatorCloudAccess/Box/BoxCloudProvider.swift
index f492c42..afc5398 100644
--- a/Sources/CryptomatorCloudAccess/Box/BoxCloudProvider.swift
+++ b/Sources/CryptomatorCloudAccess/Box/BoxCloudProvider.swift
@@ -579,7 +579,7 @@ public class BoxCloudProvider: CloudProvider {
 
 	private func convertStandardError(_ error: Error) -> Error {
 		switch error {
-		case let error as BoxAPIError where error.responseInfo.statusCode == 401:
+		case let error as BoxAPIError where (error.responseInfo.statusCode == 400 && error.responseInfo.rawBody?.contains("invalid_grant") == true) || error.responseInfo.statusCode == 401:
 			return CloudProviderError.unauthorized
 		case let error as BoxAPIError where error.responseInfo.statusCode == 404:
 			return CloudProviderError.itemNotFound
diff --git a/Sources/CryptomatorCloudAccess/Dropbox/DropboxCloudProvider.swift b/Sources/CryptomatorCloudAccess/Dropbox/DropboxCloudProvider.swift
index c104d4f..cdfd941 100644
--- a/Sources/CryptomatorCloudAccess/Dropbox/DropboxCloudProvider.swift
+++ b/Sources/CryptomatorCloudAccess/Dropbox/DropboxCloudProvider.swift
@@ -192,7 +192,7 @@ public class DropboxCloudProvider: CloudProvider {
 				}
 				if let networkError = networkError {
 					CloudAccessDDLogDebug("DropboxCloudProvider: fetchItemMetadata(at: \(cloudPath.path)) failed with networkError: \(networkError)")
-					reject(self.convertRequestErrorToDropboxError(networkError))
+					reject(self.convertRequestError(networkError))
 					return
 				}
 				guard let result = result else {
@@ -241,7 +241,7 @@ public class DropboxCloudProvider: CloudProvider {
 				}
 				if let networkError = networkError {
 					CloudAccessDDLogDebug("DropboxCloudProvider: fetchItemList(at: \(cloudPath.path)) failed with networkError: \(networkError)")
-					reject(self.convertRequestErrorToDropboxError(networkError))
+					reject(self.convertRequestError(networkError))
 					return
 				}
 				guard let result = result else {
@@ -284,7 +284,7 @@ public class DropboxCloudProvider: CloudProvider {
 					if networkError.isBadInputError(), let errorContent = networkError.errorContent, errorContent.contains("invalidPageToken") {
 						reject(CloudProviderError.pageTokenInvalid)
 					} else {
-						reject(self.convertRequestErrorToDropboxError(networkError))
+						reject(self.convertRequestError(networkError))
 					}
 					return
 				}
@@ -331,7 +331,7 @@ public class DropboxCloudProvider: CloudProvider {
 					if networkError.isClientError(), case CocoaError.fileWriteFileExists = networkError.asClientError().nsError {
 						reject(CloudProviderError.itemAlreadyExists)
 					} else {
-						reject(self.convertRequestErrorToDropboxError(networkError))
+						reject(self.convertRequestError(networkError))
 					}
 					return
 				}
@@ -395,13 +395,13 @@ public class DropboxCloudProvider: CloudProvider {
 			guard let requestError = fileUrlsToRequestErrors[localURL] else {
 				return DropboxError.unexpectedError
 			}
-			return convertRequestErrorToDropboxError(requestError)
+			return convertRequestError(requestError)
 		} else if let finishBatchRouteError = finishBatchRouteError {
 			CloudAccessDDLogDebug("DropboxCloudProvider: handleBatchUploadMissingResult(for: \(localURL)) failed with finishBatchRouteError: \(finishBatchRouteError)")
 			return DropboxError.asyncPollError
 		} else if let finishBatchRequestError = finishBatchRequestError {
 			CloudAccessDDLogDebug("DropboxCloudProvider: handleBatchUploadMissingResult(for: \(localURL)) failed with finishBatchRequestError: \(finishBatchRequestError)")
-			return convertRequestErrorToDropboxError(finishBatchRequestError)
+			return convertRequestError(finishBatchRequestError)
 		} else {
 			CloudAccessDDLogDebug("DropboxCloudProvider: handleBatchUploadMissingResult(for: \(localURL)) failed with missingResult")
 			return DropboxError.missingResult
@@ -437,7 +437,7 @@ public class DropboxCloudProvider: CloudProvider {
 					}
 					if let networkError = networkError {
 						CloudAccessDDLogDebug("DropboxCloudProvider: uploadSmallFile(from: \(localURL), to: \(cloudPath.path), mode: \(mode?.description() ?? "nil")) failed with networkError: \(networkError)")
-						reject(self.convertRequestErrorToDropboxError(networkError))
+						reject(self.convertRequestError(networkError))
 						return
 					}
 					guard let result = result else {
@@ -473,7 +473,7 @@ public class DropboxCloudProvider: CloudProvider {
 					}
 					if let networkError = networkError {
 						CloudAccessDDLogDebug("DropboxCloudProvider: createFolder(at: \(cloudPath.path)) failed with networkError: \(networkError)")
-						reject(self.convertRequestErrorToDropboxError(networkError))
+						reject(self.convertRequestError(networkError))
 						return
 					}
 					guard let result = result else {
@@ -506,7 +506,7 @@ public class DropboxCloudProvider: CloudProvider {
 				}
 				if let networkError = networkError {
 					CloudAccessDDLogDebug("DropboxCloudProvider: deleteItem(at: \(cloudPath.path)) failed with networkError: \(networkError)")
-					reject(self.convertRequestErrorToDropboxError(networkError))
+					reject(self.convertRequestError(networkError))
 					return
 				}
 				guard let result = result else {
@@ -545,7 +545,7 @@ public class DropboxCloudProvider: CloudProvider {
 					}
 					if let networkError = networkError {
 						CloudAccessDDLogDebug("DropboxCloudProvider: moveItem(from: \(sourceCloudPath.path), to: \(targetCloudPath.path)) failed with networkError: \(networkError)")
-						reject(self.convertRequestErrorToDropboxError(networkError))
+						reject(self.convertRequestError(networkError))
 						return
 					}
 					guard let result = result else {
@@ -642,26 +642,26 @@ public class DropboxCloudProvider: CloudProvider {
 		}
 	}
 
-	func convertRequestErrorToDropboxError(_ error: DBRequestError) -> DropboxError {
+	func convertRequestError(_ error: DBRequestError) -> Error {
 		if error.isHttpError() {
-			return .httpError
+			return DropboxError.httpError
 		} else if error.isBadInputError() {
-			return .badInputError
+			return DropboxError.badInputError
 		} else if error.isAuthError() {
-			return .authError
+			return CloudProviderError.unauthorized
 		} else if error.isAccessError() {
-			return .accessError
+			return DropboxError.accessError
 		} else if error.isPathRootError() {
-			return .pathRootError
+			return DropboxError.pathRootError
 		} else if error.isRateLimitError() {
 			let rateLimitError = error.asRateLimitError()
-			return .rateLimitError(retryAfter: rateLimitError.backoff.intValue)
+			return DropboxError.rateLimitError(retryAfter: rateLimitError.backoff.intValue)
 		} else if error.isInternalServerError() {
-			return .internalServerError
+			return DropboxError.internalServerError
 		} else if error.isClientError() {
-			return .clientError
+			return DropboxError.clientError
 		} else {
-			return .unexpectedError
+			return DropboxError.unexpectedError
 		}
 	}
 }
diff --git a/Sources/CryptomatorCloudAccess/Dropbox/DropboxError.swift b/Sources/CryptomatorCloudAccess/Dropbox/DropboxError.swift
index dfc0004..b515ebe 100644
--- a/Sources/CryptomatorCloudAccess/Dropbox/DropboxError.swift
+++ b/Sources/CryptomatorCloudAccess/Dropbox/DropboxError.swift
@@ -17,7 +17,6 @@ public enum DropboxError: Error {
 
 	case httpError
 	case badInputError
-	case authError
 	case accessError
 	case pathRootError
 	case rateLimitError(retryAfter: Int)
diff --git a/Sources/CryptomatorCloudAccess/GoogleDrive/GoogleDriveCloudProvider.swift b/Sources/CryptomatorCloudAccess/GoogleDrive/GoogleDriveCloudProvider.swift
index d8f6088..7a11d9f 100644
--- a/Sources/CryptomatorCloudAccess/GoogleDrive/GoogleDriveCloudProvider.swift
+++ b/Sources/CryptomatorCloudAccess/GoogleDrive/GoogleDriveCloudProvider.swift
@@ -6,6 +6,7 @@
 //  Copyright © 2020 Skymatic GmbH. All rights reserved.
 //
 
+import AppAuthCore
 import Foundation
 import GoogleAPIClientForREST_Drive
 import GRDB
@@ -532,7 +533,7 @@ public class GoogleDriveCloudProvider: CloudProvider {
 					CloudAccessDDLogDebug("GoogleDriveCloudProvider: executeQuery(\(query.requestID)) failed with error: \(error)")
 					if error.domain == NSURLErrorDomain, error.code == NSURLErrorNotConnectedToInternet || error.code == NSURLErrorCannotConnectToHost || error.code == NSURLErrorNetworkConnectionLost || error.code == NSURLErrorDNSLookupFailed || error.code == NSURLErrorResourceUnavailable || error.code == NSURLErrorInternationalRoamingOff {
 						reject(CloudProviderError.noInternetConnection)
-					} else if error.domain == kGTLRErrorObjectDomain, error.code == 401 || error.code == 403 {
+					} else if (error.domain == kGTLRErrorObjectDomain && (error.code == 401 || error.code == 403)) || (error.domain == OIDOAuthTokenErrorDomain && error.code == OIDErrorCodeOAuth.invalidGrant.rawValue) {
 						reject(CloudProviderError.unauthorized)
 					} else if error.domain == kGTLRErrorObjectDomain, error.code == 404 {
 						reject(CloudProviderError.itemNotFound)