diff --git a/96.md b/96.md
index be70999..7045431 100644
--- a/96.md
+++ b/96.md
@@ -84,7 +84,8 @@ See https://github.com/aljazceru/awesome-nostr#nip-96-file-storage-servers.
 
 ## Auth
 
-When indicated, `clients` must add an [NIP-98](98.md) `Authorization` header (**optionally** with the encoded `payload` tag set to the base64-encoded 256-bit SHA-256 hash of the file - not the hash of the whole request body).
+When indicated, `clients` must add an [NIP-98](98.md) `Authorization` header.
+`clients` SHOULD include either the `payload` tag or the `payload_multipart` tag with the `file` multipart field name included in the digest (`["payload_multipart", "<sha256-of-file>", "file"]`).
 
 ## Upload
 
diff --git a/98.md b/98.md
index be425b2..dbb78bc 100644
--- a/98.md
+++ b/98.md
@@ -43,12 +43,27 @@ Servers MUST perform the following checks in order to validate the event:
 3. The `u` tag MUST be exactly the same as the absolute request URL (including query parameters).
 4. The `method` tag MUST be the same HTTP method used for the requested resource.
 
-When the request contains a body (as in POST/PUT/PATCH methods) clients SHOULD include a SHA256 hash of the request body in a `payload` tag as hex (`["payload", "<sha256-hex>"]`), servers MAY check this to validate that the requested payload is authorized.
+When the request contains a body (as in POST/PUT/PATCH methods) clients SHOULD include a SHA256 hash of the request body in a `payload` tag as hex (`["payload", "<sha256-hex>"]`) or a SHA256 hash of the relevant fields in a `payload_multipart` tag.
+Servers MAY check these to validate that the requested payload is authorized.
 
 If one of the checks was to fail the server SHOULD respond with a 401 Unauthorized response code.
 
 Servers MAY perform additional implementation-specific validation checks.
 
+### The `payload_multipart` tag
+
+The `payload_multipart` tag SHOULD only be sent when authorizing a request with a `Content-Type` of `multipart/form-data`.
+A valid `payload_multipart` tag will always consist of 3 or more elements.
+The first element is always the tag name, `payload_multipart`.
+The second element is the sha256 hash, which is computed over the concatenation of every serialized multipart field, in order.
+The third through last elements name the form fields which will be concatenated together to calculate the hash.
+
+`["payload_multipart", "<sha256-hex-of-concatenated-fields>", "<multipart-field-name-0>", ..."<multipart-field-name-N>"]`
+
+The multipart-field-names MUST appear in the same order as they appear in the multipart body.
+Repeated field names MUST have corresponding repeated fields in the multipart body.
+After a multipart field is added to the sha256 digest, no subsequent multipart-field-name may refer to any multipart field up to and including the one which was just processed (field processing always progresses forward in the request body, never backwards).
+
 ## Request Flow
 
 Using the `Authorization` HTTP header, the `kind 27235` event MUST be `base64` encoded and use the Authorization scheme `Nostr`