# AuthenticationAttemptIdentifier

Location: [gRPC API](https://developer.m-files.com/APIs/gRPC-API/index.md) > [Reference](https://developer.m-files.com/APIs/gRPC-API/Reference/index.md) > [Messages](https://developer.m-files.com/APIs/gRPC-API/Reference/Messages/index.md)

HTML version: https://developer.m-files.com/APIs/gRPC-API/Reference/Messages/MFiles.AuthenticationAttemptIdentifier/

Identifies one login attempt that spans several [LogIn](https://developer.m-files.com/APIs/gRPC-API/Reference/MFiles.IRPCLogin/LogIn/index.md) calls.
Copy it from the response to the next request unchanged.

- **Full name:** `MFiles.AuthenticationAttemptIdentifier`
- **Proto file:** [`mfiles/structs.proto`](https://developer.m-files.com/APIs/gRPC-API/downloads/proto/mfiles/structs.proto)

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## Fields

| Field | Type | Number | Description |
|---|---|---|---|
| <a id="f-legacy_data"></a>`legacy_data` | `uint32` | 1 | Short identifier, used when the client does not set `ClientCapabilities.long_authentication_attempt_identifier`. |
| <a id="f-data"></a>`data` | `bytes` | 2 | 32-byte identifier, used when the client sets `ClientCapabilities.long_authentication_attempt_identifier`; otherwise all zeros. |

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## Used in fields

- [`AuthDataClientUnion.MFilesLeg2Data.authentication_attempt_identifier`](https://developer.m-files.com/APIs/gRPC-API/Reference/Messages/MFiles.AuthDataClientUnion/index.md#t-MFilesLeg2Data-authentication_attempt_identifier): The identifier returned by the first step, unchanged.
- [`AuthDataClientUnion.WindowsData.authentication_attempt_identifier`](https://developer.m-files.com/APIs/gRPC-API/Reference/Messages/MFiles.AuthDataClientUnion/index.md#t-WindowsData-authentication_attempt_identifier): Unset in the first call; in later calls, the identifier from the previous response.
- [`AuthDataClientUnion.PluginData.authentication_attempt_identifier`](https://developer.m-files.com/APIs/gRPC-API/Reference/Messages/MFiles.AuthDataClientUnion/index.md#t-PluginData-authentication_attempt_identifier): Unset in the first call; in later calls, the identifier from the previous response.
- [`AuthDataServer.authentication_attempt_identifier`](https://developer.m-files.com/APIs/gRPC-API/Reference/Messages/MFiles.AuthDataServer/index.md#f-authentication_attempt_identifier): Identifies this login attempt. In multi-step methods, send it back in the next call, in the `authentication_attempt_identifier` field of the request's union member. Ignore it for `AUTH_DATA_TYPE_CREDENTIALS`.