Use wget instead of curl to submit attachment

This does exactly what I want it to:

curl -X POST http://example.com/xyz -d '{"_id":"123", "_attachments":{"foo.txt":{"content_type":"text\/plain","data": "VGhpcyBpcyBhIGJhc2U2NCBlbmNvZGVkIHRleHQ="}}}' -H "Content-Type: application/json"

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It submits "This is a base64 encoded text" as an attachment.  

How can I do exactly the same thing but with wget instead of cURL?