Sending Form-Data in Apex Callout to Auth0?

Question:

I need to send a multipart/form-data request from Salesforce Apex to Auth0’s /api/v2/jobs/users-imports endpoint. I have limited experience working with form-data requests.

I structured the request body as follows:

--usersjiaosd9821931-FGGHJ
Content-Disposition: form-data; name="users"; filename="users.json";

Content-Type: application/json

[{"email": "ian+3@gmail.com","password": "alwaysPostFakePasswords"}, {"email": "ian+4@gmail.com","password": "sdfnDAqpAdoQF&www344"}]
--usersjiaosd9821931-FGGHJ
Content-Disposition: form-data; name="connection_id"

con_test
--usersjiaosd9821931-FGGHJ--

My Apex code:

Http http = new Http();
HttpRequest request = new HttpRequest();
request.setEndpoint('The url to /api/v2/jobs/users-imports');
request.setMethod('POST');
request.setHeader('Accept', 'application/json');
request.setHeader('Content-Type', 'multipart/form-data; boundary=--usersjiaosd9821931-FGGHJ');
request.setBody(body);
HttpResponse response = http.send(request);
System.debug(response.getBody());

However, I keep getting this error response:

{"statusCode":400,"error":"Bad Request","message":"Must provide 'users' file as multipart part.","errorCode":"invalid_body"}

What is wrong with my request, and how can I properly format it in Apex?

Answer:

The issue is likely due to improper formatting of the multipart request in Apex. Unlike other content types, multipart/form-data requires properly structured boundaries, correct handling of file uploads, and proper encoding of each part.

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Use Blob for File Upload

Apex requires setting the body using Blob when sending files in multipart/form-data. Try this approach:

Http http = new Http();
HttpRequest request = new HttpRequest();
request.setEndpoint('The url to /api/v2/jobs/users-imports');
request.setMethod('POST');

String boundary = 'usersjiaosd9821931-FGGHJ';
request.setHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);

String body = '--' + boundary + '\r\n' +
    'Content-Disposition: form-data; name="users"; filename="users.json"\r\n' +
    'Content-Type: application/json\r\n\r\n' +
    '[{"email": "ian+3@gmail.com","password": "alwaysPostFakePasswords"}, ' +
    '{"email": "ian+4@gmail.com","password": "sdfnDAqpAdoQF&www344"}]' +
    '\r\n--' + boundary + '\r\n' +
    'Content-Disposition: form-data; name="connection_id"\r\n\r\n' +
    'con_test\r\n' +
    '--' + boundary + '--';

request.setBodyAsBlob(Blob.valueOf(body));

HttpResponse response = http.send(request);
System.debug(response.getBody());

Explanation: The code constructs a multipart/form-data HTTP request in Apex to send a user import request to Auth0. It defines a boundary string to separate form fields, formats the request body correctly with Content-Disposition headers, and includes both a JSON file (users.json) and a connection_id parameter. Finally, it converts the body to a Blob using setBodyAsBlob to ensure proper encoding before sending the request.

Summing Up

When sending multipart/form-data from Apex to Auth0, ensure correct boundary formatting, proper content disposition, and use setBodyAsBlob for file uploads. The error occurs because the API expects a well-structured file part, which requires precise \r\n line breaks and encoding. Fixing the request involves correctly structuring the body, using a Blob, and ensuring the right headers. Properly formatted requests prevent 400 Bad Request errors and ensure seamless API communication.

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