Add Batch Query REST API

[nevumx]

What is the underlying problem you're trying to solve?

Currently, if we have several resources or queries we want to authorize via the HTTP REST API without incurring several round-trip network penalties, there is really only one option, which is to pack them in an array that is POSTed to the normal Query REST API with a URL like http://localhost:8181/v1/data/play/batch, like so:

{
    "input": [
        {"principal": "alice", "action": "read_compensation", "entity": "bob"},
        {"principal": "alice", "action": "read_compensation", "entity": "charlie"}
    ]
}

and then process them through a policy like:

package play

import rego.v1

default allow := false

allow if input == {"principal": "alice", "action": "read_compensation", "entity": "charlie"}

batch := [result |
	some query in input
	result := allow with input as query
]

getting back a result like,

{
    "decision_id": "c7703c24-9eba-44e2-ab05-cbd720ec1d19",
    "result": [
        false,
        true
    ]
}

Example playground: https://play.openpolicyagent.org/p/US8tNMq5wa

While this does work at first, when decision logs for such batch queries are uploaded to a service like Styra DAS, they quickly become unreadable if 10 or 100 or more queries are evaluated as a part of a single batch query.

One strategy to attempt to fix this is to just funnel each individual query into its own query with http.send(...), like so:

batch := [result |
	some query in input
	result := http.send({"method": "POST", "url": "http://localhost:8181/v1/data/play/allow", "body": {"input": enriched_query}}).body.result
]

...And then the batch query logs can be filtered out with some log policies. However, as can perhaps be expected, in practice, this has been found to incur a 5x performance penalty, (i.e. a 100ms query would turn into a 500ms query) likely due to unnecessary serialization/deserialization and traversal of the network stack.

Describe the ideal solution

An ideal solution would be a Batch Query REST API where we could POST an HTTP REST request to a special url like http://localhost:8181/v1/batch/data/play/allow in an array of inputs like so:

{
    "inputs": [
        {"principal": "alice", "action": "read_compensation", "entity": "bob"},
        {"principal": "alice", "action": "read_compensation", "entity": "charlie"}
    ]
}

getting back a result like,

{
    "decision_id": "c7703c24-9eba-44e2-ab05-cbd720ec1d1a",
    "results": [
        false,
        true
    ]
}

and in addition, it would produce a decision log for each query in the array that could then be sent to a service like Styra DAS.

Describe a "Good Enough" solution

In a "Good Enough" solution, we would have a built-in function like:

batch := [result |
	some query in input
	result := opa.evaluate(query) # or perhaps opa.evaluate(path, query) where `path` looks like "/v1/data/play/allow"
]

Which would simply evaluate the argument passed to it as if it came from the HTTP REST Query API, but without needing to run all the serialization/deserialization/network code that would otherwise be needed, however it would produce the associated decision log.

Additional Context

N/A

[stale]

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