---
title: "Authenticate on Android"
description: "Authenticate a merchant with the Android reader SDK using OAuth or native login."
image: "https://developer.sumup.com/og/index.png"
---

> Documentation Index
> Fetch the complete documentation index at: https://developer.sumup.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Authenticate on Android

After [initializing the reader SDK](/terminal-payments/sdks/android/setup/), authenticate the merchant before opening reader settings or starting checkout.

## Transparent authentication

Use the [OAuth 2.0 authorization code flow](/tools/authorization/oauth/#authorization-code-flow) to obtain an access token for the merchant. Pass it to the SDK to log in without showing the SDK's login screen.

```java
SumUpLogin sumupLogin = SumUpLogin.builder(mAffiliateKey).accessToken("MY_ACCESS_TOKEN").build();
SumUpAPI.openLoginActivity(MainActivity.this, sumupLogin, 1);
```

For information about how to obtain a token, please see the [Authorization Documentation](/tools/authorization/).

If the token is invalid, `SumUpAPI.Response.ResultCode.ERROR_INVALID_TOKEN` is returned.

## Retrieve data of the active merchant account

Call `getCurrentMerchant()` to read the logged-in merchant's details. Check `isLoggedIn()` first.

```java
	if (!SumUpAPI.isLoggedIn()) {
		// no merchant account currently logged in
	} else {
		Merchant currentMerchant = SumUpAPI.getCurrentMerchant();
	}
```

## Logging merchant in and out

:::caution
Native login uses the user's default merchant account and does not offer an account selector. For users with access to multiple merchant accounts, we recommend using a managed user account created in the intended merchant. Alternatively, set the default merchant account before logging in. See [merchant account setup for native SDK login](/terminal-payments/quickstart/#users-with-multiple-merchant-accounts).
:::

To display the SDK's login screen, create a login request with your [Affiliate Key](/tools/authorization/affiliate-keys/):

```java
SumUpLogin sumupLogin = SumUpLogin.builder(mAffiliateKey).build();
SumUpAPI.openLoginActivity(MainActivity.this, sumupLogin, 1);
```

To integrate with the Activity Result API, use `SumUpLoginContract`:

```kotlin
val loginLauncher = registerForActivityResult(SumUpLoginContract()) { result ->
        // Login result
    }
loginLauncher.launch(sumupLogin)
```

![Login screen](</img/guides/android_sdk_login.png>)

> **Note**
>
> For new production integrations, use [OAuth authentication](/terminal-payments/sdks/android/authentication/#transparent-authentication).

Log out before switching merchant accounts:

```java
SumUpAPI.logout();
```

## Next step

[Connect and manage a card reader](/terminal-payments/sdks/android/readers/). For the separate Tap to Pay SDK, use its [authentication instructions](/terminal-payments/sdks/android/tap-to-pay/#authentication).

Source: https://developer.sumup.com/terminal-payments/sdks/android/authentication/index.mdx