DNA Auth Resolver

A simple configuration-based module for inter-network RPC in Holochain hApps.

• About
• Usage
  • In the origin zome
  • In the destination DNA
  • Troubleshooting
• Building / developing
• Built with this module
• License

About

(TLDR; this module replaces what was formerly known as "bridging" in Holochain-Redux.)

You have a Holochain application composed of multiple coordinated application 'cells'. These cells want to talk to each other but need some way of assigning capabilities to each other in order to do so. This helper module and related zome provides this functionality.

It works by providing a layer for mapping pre-known request identifiers onto the actual zome & method names deployed into a DNA. An open-access endpoint living at the pre-known remote_auth zome name in the destination DNA is used to request and assign separate capability tokens which can be retrieved and used at runtime to authenticate method calls between apps.

Usage

In the origin zome

(the one where a record has been modified which will trigger an update in some destination zome in a remote DNA)

1. Include the hc_zome_dna_auth_resolver_storage crate in the zome module to ensure that its capability storage EntryDef is available:

   [dependencies]
   hc_zome_dna_auth_resolver_storage = {git = "https://github.com/holochain-open-dev/dna-auth-resolver", tag = "X.X.X" package = "hc_zome_dna_auth_resolver_storage"}

   use hc_zome_dna_auth_resolver_storage::*;

2. Wherever your cross-DNA logic is triggered, import the _lib crate and use the helper methods to communicate with the remote zome:

   [dependencies]
   hc_zome_dna_auth_resolver_lib = {git = "https://github.com/holochain-open-dev/dna-auth-resolver", tag = "X.X.X" package = "hc_zome_dna_auth_resolver_lib"}

   use hc_zome_dna_auth_resolver_lib::{DNAConnectionAuth, ensure_authed};
   
   // define external permission ID to map to in destination zome config
   pub const remote_permission_id: &str = "EXTERNAL_PERMISSION_IDENTIFIER";
   
   // pull destination DNA hash from somewhere
   let to_dna: DnaHash = //...
   
   // transparently request & retrieve auth data for remote DNA/zome
   let auth_data = ensure_authed(to_dna, remote_permission_id)?;
   
   // use auth data to make request
   let DNAConnectionAuth { claim, method } = auth_data;
   let resp = hdk::call(
   	Some(CellId::new(to_dna, claim.grantor().to_owned())), 
   	method.0, method.1, 
   	Some(claim.secret().to_owned()), 
   	payload,
   );

In the destination DNA

(the one containing the zome being "driven" by the origin DNA/zome)

1. Build and include a compiled-to-WASM version of the hc_zome_dna_auth_resolver crate, with the name remote_auth. The zome name is important.
   1. One possible way of doing this is to re-export the crate from this module in your own derived crate:

      [package]
      name = "hc_zome_my_app_auth_resolver"
      version = "0.1.0"
      edition = "2018"
      private = true
      
      [dependencies]
      hc_zome_dna_auth_resolver = {git = "https://github.com/holochain-open-dev/dna-auth-resolver", tag = "X.X.X", package = "hc_zome_dna_auth_resolver"}
      
      [lib]
      path = "src/lib.rs"
      crate-type = ["cdylib", "rlib"]

      extern crate hc_zome_dna_auth_resolver;

   2. Include the built zome artifacts in your DNA bundle, along with the destination zomes.

      zomes:
        # ...
        - name: remote_auth
          bundled: "../../target/wasm32-unknown-unknown/release/hc_zome_my_app_auth_resolver.wasm"

2. Add this configuration block to the DNA properties:

   properties:
     # ...
     remote_auth:
       permissions:
    	 - extern_id: EXTERNAL_PERMISSION_IDENTIFIER
    	   allowed_method: [TARGET_ZOME_NAME, TARGET_FUNC_NAME]

Troubleshooting

Errors relating to missing EntryDef for "dna_authed_method_mapping":

This can happen for zomes which define the entry_defs extern themselves rather than using convenience macros; in which case any entry types defined with #[hdk_entry] are overridden by the returned array.

In such cases, you can add this EntryDef to your EntryDefsCallbackResult:

EntryDef {
	id: CAP_STORAGE_ENTRY_DEF_ID.into(),
	visibility: EntryVisibility::Private,
	crdt_type: CrdtType,
	required_validations: 1.into(),
	required_validation_type: RequiredValidationType::default(),
},

Building / developing

Written in Rust. Uses regular Cargo manifests & package commands, best included as dependencies in your other packages.

To reference these crates directly from Github, you can use (eg.)

hc_zome_dna_auth_resolver_lib = {git = "https://github.com/holochain-open-dev/dna-auth-resolver", tag = "X.X.X" package = "hc_zome_dna_auth_resolver_lib"}

Built with this module

hdk_records is a high-level record and index management library for highly modular Holochain apps.

License

Apache-2.0