Facebook Login

If using Expo, first you need to follow the setup instructions.

https://docs.expo.io/versions/latest/sdk/facebook

tl;dr

{
  "expo": {
    "sdkVersion": "27.0.0",
    "privacy": "unlisted",
    "name": "Exposition",
    "icon": "./assets/icon.png",
    "version": "1.0.0",
    "slug": "nodular-exposition",
    "facebookScheme": "<% fromFacebook %>",
    "facebookAppId": "<% fromFacebook %>",
    "facebookDisplayName": "Exposition",
    "ios": {
      "bundleIdentifier": "com.nodular.exposition"
    },
    "android": {
      "package": "com.nodular.exposition"
    }
  }
}
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FB.login(function(response) {
  // Check if the user logged in successfully.
  if (response.authResponse) {
    console.log('You are now logged in.');

    // Add the Facebook access token to the Cognito credentials login map.
    AWS.config.credentials = new AWS.CognitoIdentityCredentials({
      IdentityPoolId: 'IDENTITY_POOL_ID',
      Logins: {
        'graph.facebook.com': response.authResponse.accessToken
      }
    });

    // Obtain AWS credentials
    AWS.config.credentials.get(function() {
      // Access AWS resources here.
    });
  } else {
    console.log('There was a problem logging you in.');
  }
});
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