-get-gcp-jwt: produce a JWT for use in GCP Storage

pkg/arvo/ted/get-gcp-jwt.hoon

@@ -0,0 +1,134 @@
+::  Thread that gets a JWT for use with Google Storage.
+::
+::  This thread expects settings-store to contain relevant fields from a GCP
+::  service account JSON file, e.g. as poked by urbit/sh/poke-gcp-account-json.
+::  Specifically, it depends on the `token_uri`, `client_email`,
+::  `private_key_id`, and `private_key` fields. If these fields are not in
+::  settings-store at the time the thread is run, it will fail.
+::
+::  The thread works by first constructing a self-signed JWT using the fields
+::  in settings-store. Then, it sends this JWT to the specified token URI
+::  (usually https://oauth2.googleapis.com/token), which gives us a JWT signed
+::  by Google. This token can then be used as a bearer token for requests to
+::  Google Storage.
+::
+::  The returned token has an expiration time of 60 minutes after the time at
+::  which the thread was called.
+::
+::
+/-  spider, settings
+/+  jose, pkcs, strandio
+=,  strand=strand:spider
+=,  format
+=,  jose
+=,  pkcs
+^-  thread:spider
+|^
+|=  *
+=/  m  (strand ,vase)
+^-  form:m
+;<  =bowl:spider  bind:m  get-bowl:strandio
+;<  iss=@t        bind:m  (read-setting %client-email)
+;<  =key:rsa      bind:m  read-private-key
+;<  kid=@t        bind:m  (read-setting %private-key-id)
+;<  aud=@t        bind:m  (read-setting %token-uri)
+=/  sot=@t
+  %:  self-jwt
+    key  kid  iss
+    'https://www.googleapis.com/auth/devstorage.editor'
+    aud  now.bowl
+  ==
+;<  jot=@t  bind:m  (sign-jwt sot aud)
+(pure:m !>(jot))
+::
+++  read-setting
+  |=  key=term
+  =/  m  (strand @t)  ^-  form:m
+  ;<  has=?  bind:m
+    (scry:strandio ? /gx/settings-store/has-entry/gcp-store/[key]/noun)
+  ?.  has
+    (strand-fail:strandio %no-setting key ~)
+  ;<  =data:settings  bind:m
+    %+  scry:strandio
+      data:settings
+    /gx/settings-store/entry/gcp-store/[key]/settings-data
+  ?>  ?=([%entry %s @] data)
+  (pure:m p.val.data)
+::
+++  read-private-key
+  =/  m  (strand ,key:rsa)  ^-  form:m
+  ;<  dat=@t  bind:m  (read-setting %private-key)
+  %-  pure:m
+  %.  dat
+  ;:  cork
+    to-wain:format
+    ring:de:pem:pkcs8
+    need
+  ==
+::  construct and return a self-signed JWT issued now, expiring in ~h1.
+::  TODO: maybe move this into lib/jose/hoon
+::
+++  self-jwt
+  |=  [=key:rsa kid=@t iss=@t scope=@t aud=@t iat=@da]
+  ^-  @t
+  =/  job=json
+    %^  sign:jws  key
+      ::  the JWT's "header"
+      %:  pairs:enjs
+        alg+s+'RS256'
+        typ+s+'JWT'
+        kid+s+kid
+        ~
+      ==
+    ::  the JWT's "payload"
+    %:  pairs:enjs
+      iss+s+iss
+      sub+s+iss                                 ::  per g.co, use iss for sub
+      scope+s+scope
+      aud+s+aud
+      iat+(sect:enjs iat)
+      exp+(sect:enjs (add iat ~h1))
+      ~
+    ==
+  ?>  ?=([%o *] job)
+  =*  mep  p.job
+  =+  :~  pod=(sa:dejs (~(got by mep) 'protected'))
+          pad=(sa:dejs (~(got by mep) 'payload'))
+          sig=(sa:dejs (~(got by mep) 'signature'))
+      ==
+  %-  crip                                      ::  XX
+  :(weld pod "." pad "." sig)
+::  RPC to get a signed JWT. Probably only works with Google.
+::  Described at:
+::  https://developers.google.com/identity/protocols/oauth2/service-account
+::
+++  sign-jwt
+  |=  [jot=@t url=@t]
+  =/  m  (strand @t)  ^-  form:m
+  ;<  ~  bind:m
+    %:  send-request:strandio
+      method=%'POST'
+      url=url
+      header-list=['Content-Type'^'application/json' ~]
+      ^=  body
+      %-  some  %-  as-octt:mimes:html
+      %-  en-json:html
+      %:  pairs:enjs
+        ['grant_type' s+'urn:ietf:params:oauth:grant-type:jwt-bearer']
+        assertion+s+jot
+        ~
+      ==
+    ==
+  ;<  rep=client-response:iris  bind:m
+    take-client-response:strandio
+  ?>  ?=(%finished -.rep)
+  ?~  full-file.rep
+    (strand-fail:strandio %no-response ~)
+  =/  body=@t  q.data.u.full-file.rep
+  =/  jon=(unit json)  (de-json:html body)
+  ?~  jon
+    (strand-fail:strandio %bad-body ~[body])
+  ?.  ?=([%o [[%'id_token' %s @] ~ ~]] +.jon)
+    (strand-fail:strandio %bad-json ~[body])
+  (pure:m p.q.n.p.u.jon)
+--