In the Amplify documentation, under the Storage/File access levels section there is a paragraph that states:
Files are stored under private/{user_identity_id}/ where the user_identity_id corresponds to the unique Amazon Cognito Identity ID for that user.
How to fetch user_identity_id from the lambda function?
Request to the lambda is authorized, the event.requestContext.authorizer.claims object is available, I can see the user data, but not the user_identity_id.
EDIT: Now I see that there is a field event.requestContext.identity.cognitoIdentityId, but the value is null. Still need to find the way to fetch it.
Ok, so there's no right way to map Cognito identity ID and Cognito user. There is a lengthy discussion here where a couple of workarounds can be found. For now, I'm going to use this solution where, instead of identity_id, you can specify a custom attribute (most likely a sub) as a folder name.
EDIT: There is another solution that might help (found somewhere on the internet, and I verified that it works)
const AWS = require('aws-sdk')
const cognitoIdentity = new AWS.CognitoIdentity();
function getCognitoIdentityId(jwtToken) {
const params = getCognitoIdentityIdParams(jwtToken);
return cognitoIdentity
.getId(params)
.promise()
.then(data => {
if (data.IdentityId) {
return data.IdentityId;
}
throw new Error('Invalid authorization token.');
});
}
function getCognitoIdentityIdParams(jwtToken) {
const loginsKey = `cognito-idp.${process.env.REGION}.amazonaws.com/${process.env.USERPOOLID}`;
return {
IdentityPoolId: `${process.env.IDENTITY_POOL_ID}`,
Logins: {
[loginsKey]: jwtToken,
},
};
}
If the user accesses the lambda through graphql via the AppSync service then the identity is stored event.identity.owner
Here is some typescript code I use to pull the user_identity_id from the event. However, the user doesn't always call the lambda direct sp the user_identity can also be based in if from an authorized IAM role.
export function ownerFromEvent(event: any = {}): string {
if (
event.identity.userArn &&
event.identity.userArn.split(":")[5].startsWith("assumed-role")
) {
// This is a request from a function over IAM.
return event.arguments.input.asData.owner;
} else {
return event.identity.owner;
}
}