align account_state HTTP protobuf fields with stock GMS

[zappybiby]

Summary

This PR corrects the protobuf field numbers used by microG's HTTP account_state request.

The request schema added by #3420 currently encodes:

nested field 1 = com.google.android.gms
nested field 2 = Google certificate SHA-1
nested field 3 = absent

Stock Google Play services encodes the same HTTP request as:

nested field 1 = absent
nested field 2 = com.google.android.gms
nested field 3 = Google certificate SHA-1

Stock HTTP schema

The stock HTTP layout is:

message AccountStateHttpClientInfo {
  // Field 1 is unset.
  optional string packageName    = 2;
  optional string appCertSha1Hex = 3;
}
message AccountStateHttpRequest {
  optional AccountStateHttpClientInfo clientInfo = 1;
}

Google Play versions checked:

• Build: 26.26.62 (100400-945452815)
• Build: 26.14.34 (040400-899752054)
• Build: 25.08.34 (260800-739221510)

All tested versions send:

field 1 = absent
field 2 = package name
field 3 = certificate digest

The completed nested message is then placed in outer field 1 before the HTTP POST is created.

Field 1 appears to be a legacy AccountManager-stored account credential field. I found it in decompiles of old versions like 20.15.15 and 20.12.16.

evidence

A public dataset contains three decoded stock requests with:

• Google Play services: 24.47.38

Source repository: https://github.com/doug-leith/cookies-etc-stored-by-google-android

All three request bodies decode identically:

1 {
  2: "com.google.android.gms"
  3: "38918a453d07199354f8b19af05ec6562ced5788"
}

The stock AANG application header uses:

field 1 = package name
field 2 = certificate SHA-1
field 3 = request/network enum

The stock HTTP client-information message:

field 1 = absent
field 2 = package name
field 3 = certificate SHA-1

Runtime test

The HTTP request was tested on Android API 36 with an instrumented GmsCore build.
The request used:

• Endpoint: https://android.googleapis.com/auth/lookup/account_state?rt=b

Mode	Nested body	Result
pr_fields_1_2	Package in 1; certificate in 2	Success
stock_fields_2_3	Package in 2; certificate in 3	Success
header_empty	Outer field 1 with empty nested message	Success
bogus_stock_fields	Invalid package/certificate in 2 and 3	Success
body_absent	No outer protobuf request	IOException

Every successful request returned identical data.

effect

The field-number mismatch did not change the response in the auth flow.

This explains why the current implementation works despite not matching the stock format.