AWS S3 Generate a presigned url with a md5 check - amazon-web-services

Question

Im looking to generate a pre signed url with aws s3.
It works fine with some condition (mime type for example) but im unable to use 'Content-MD5'.
I use the node js sdk and put the md5 in fields object.
const options = {
Bucket: bucket,
Expires: expires,
ContentType: 'multipart/form-data',
Conditions: [{ key }],
Fields: {
'Content-MD5': params.md5,
},
} as PresignedPost.Params;
if (acl) {
options.Conditions.push({ acl });
}
if (params.mimeType) {
options.Conditions.push({ contentType: params.mimeType });
}
But after when I upload the file, I would like AWS to check by itself the uploaded file with the MD5 given in the presigned request but I always have that error :
<?xml version="1.0" encoding="UTF-8"?>
<Error>
<Code>AccessDenied</Code>
<Message>Invalid according to Policy: Policy Condition failed: ["eq", "$Content-MD5", "<md5>"]</Message>
<RequestId>497312AFEEF83235</RequestId>
<HostId>KY9RxpGZzRog7hjlDk3whjAbItG/mwhpItYDL7rUNNH4BCXMfmLZsbZIPKivmSZZ3VkWxlgstOk=</HostId>
</Error>
My MD5 is generated like that in the browser ( just after recording a video ):
const reader = new FileReader();
reader.readAsBinaryString(blob);
reader.onloadend = () => {
const mdsum = CryptoJS.MD5(reader.result.toString());
resolve(CryptoJS.enc.Base64.stringify(mdsum));
};
Maybe it's not the way it works ?
edit :
If I add to the upload form data (md5 hash is the same as set in the presigned)
formData.append('Content-MD5', encodeURI(fields['Content-MD5']));
the error becomes
<?xml version="1.0" encoding="UTF-8"?>
<Error>
<Code>BadDigest</Code>
<Message>The Content-MD5 you specified did not match what we received.</Message>
<ExpectedDigest>2b36c76525c8d3a6dada59a6ad2867a7</ExpectedDigest><CalculatedDigest>+RifURVLd61O6QCT+SzhBg==</CalculatedDigest><RequestId>B4FF38D0FCC2E8F2</RequestId><HostId>yS7q200rJpBu48RNcGzsb1oGbDUrN8UK9+gkg6jGMl+EJSGeyQaSCfwfcMRUeNlJYapfmF304Oc=</HostId></Error>
answer:
const reader = new FileReader();
reader.readAsBinaryString(blob);
reader.onloadend = () => {
resolve(CryptoJS.enc.Base64.stringify(CryptoJS.MD5(CryptoJS.enc.Latin1.parse(reader.result.toString()))));
};