Simple Page-Owner Token (SPOT) Authentication

Just wanted to highlight this interesting work from sandro

https://github.com/sandhawke/spot/blob/master/spec.md

This document specifies an HTTP authentication mechanism suitable for use
in situations where the HTTP client is tightly coupled with another HTTP
server. It is very easy to implement and requires no extra crypto.

For illustration purposes, we'll say Alice is a process which serves the
web resource at http://alice.example/alice and wants to act as a client to
access a protected resource http://bob.example/bob, which is served by a
different process, Bob.

For non-trivial use, to provide some resistance against attackers who can
view or intercept network traffic or subvert the DNS, HTTPS URIs should be
used, and clients should check that the server DNS name matches the
certificate.
 Status

Not yet implemented.

Before wide deployment, the new authentication type Page-Owner-Token and
the two new HTTP headers (Page-Owner-Token-Check and Page-Owner-Token-OK)
should be registered with the IETF.
 Walkthrough

*Step 1.* Alice performs an HTTP GET on an access-controlled page served by
Bob, but does not authenticate herself, so Bob returns a 401 error. The
response includes a header telling Alice she can authenticate using this
protocol and try again.

> GET /bob HTTP/1.1
> Host: bob.example
...
< HTTP/1.1 401 Authorization Required
< WWW-Authenticate: Page-Owner-Token
...

This uses the standard WWW-Authenticate HTTP header with a new keyword for
this new authentication type.

*Step 2.* Alice generates a cryptographicly random token, a nonce. In this
example, I'll write it as xyz123. It should use only the Base64 characters.

*Step 3.* Alice repeats the GET, this time including a header which
identifies her via a web page and includes the nonce:

> GET /bob HTTP/1.1
> Host: bob.example
> Authorization: Page-Owner-Token client="http://alice.example/alice" token="xyz123"
...

ISSUE: Should it just be http://alice.example/ ? What does it mean to
include the /alice?

Alice can include multiple headers like this, since it might be that only
one of her multiple identies actually has access to /bob and she doesn't
now which. The identity strings must be dereferenceable. They can be either
an Information resource IRI (returning 200 OK) or a non-information
resource IRI (returning 303, or having a hash). Either works fine for this
protocol.

Note that sending identity strings like this may reveal more to Bob than
desirable.

*Step 4.* Bob checks to see if the request provides a valid token:

> HEAD /alice HTTP/1.1
> Host: alice.example
> Page-Owner-Token-Check: token="xyz123" relying-party="http://bob.example/bob"
...

The verb could be GET (instead of HEAD) if the Bob is interested in the
content of /alice.

*Step 5.* Alice confirms:

< HTTP/1.1 200 OK
< Page-Owner-Token-OK: true
< Set-Cookie: [whatever, optional]
...

Alice only does this if the token was in fact the one she generated for her
GET to Bob.

Only a response containing the header "Page-Owner-Token-OK: true" is taken
as confirmation.

The Set-Cookie is an optional shortcut. With this cookie, Alice can give
Bob some secret to use in future communications, so that Bob can act as an
HTTP client accessing alice.example in the future without needing to go
through his own SPOT handshake.

*Step 6.* Bob returns the protected content requested in Step 3

< HTTP/1.1 200 OK
< Set-Cookie: [whatever, optional]
... content ...

The Set-Cookie is an optional shortcut. With this cookie, Bob can give
Alice some secret to use in future communications, so that Alice and Bob do
not have to repeat this handshake every time.