Add optional "method", "headers", and "body" fields to Item AssetObject

[indiejames]

Currently Assets only support an "href" field that can be used to retrieve data. At times a download may require an HTTP method other than GET, e.g., POST, especially if there are parameters involved that cannot fit into a URL, in which case a body is needed. Similarly, a download may require specific headers to be set.

Link Objects support all of these via the "method", "headers", and "body" optional fields. It makes sense to add these as optional fields to Asset Objects as well.

This could potentially be done as an extension, but that is less likely to be supported by libraries, so it would probably be better if this were part of the core spec.

[m-mohr]

This would make normal downloads in browsers difficult to impossible.

[emmanuelmathot]

In my opinion, those fields should likely be placed in the free storage fields. If a header needs to be set, it is probably related to a function (e.g., authentication) that has its own extension.

[m-mohr]

What are the use cases? Could people collect and describe those here?

[indiejames]

@m-mohr the use case we have is that some of the data we generate STAC items for require many parameters for the download, so can only be reached via a POST (the URL with query parameters would be too long). Specifically, some Open DAP links.

@emmanuelmathot if I am remembering correctly what you mean by "free storage fields", those could be used internally, but would not be supported by libraries like pystac.