# Macaroon
[](https://coveralls.io/github/doawoo/macaroon?branch=main)
Cookies but better. For Elixir.
If you'd like to know all the details about Macaroons, I encourage you to read the [research paper](https://research.google/pubs/pub41892/)!
I'll summarize it up a bit below:
## What are they?
### Basic Summary
Macaroons are bearer credentials, similar to cookies, API tokens, or JWTs. They're presented upon each of a client's request. Where Macaroons differ from most bearer credentials are the fact that they securely embed caveats (permissions, reasons, capabilities, etc.) inside the credential itself. These caveats are signed using a secret key, so the target service can trust the credential as it is presented along with the client's request. The target service can evaluate the request, and the caveats to see if the operation is allowed.
### Caveats
Caveats are simple statements that define what capabilities, identities, or authority the Macaroon holds.
Here's an example list of caveats a Macaroon may hold pertaining to an imaginary file sharing service:
```
1. user_id = 1234
2. user_upload_limit = 4MB
3. user_download_limit = 100MB
4. upload_namespace=/users/1234/*
5. timestamp <= 1/10/2021-5:48:47PM
```
With the examples above, the service should respect the requested operation should it meet the Macaroon's declared and signed caveats.
These caveats can contain any information in any string-based format. It's up to the service author to design the predicate language used.
### Verification
When operating a service, you can verify a Macaroon "exactly" or "generally".
Exact verification means the data of the caveat must match byte-per-byte.
General verification allows the service author to provide simple callbacks which receive the caveat and can return `true` or `false` to indicate if it is met.
### Discharging
TODO
## Examples
### Creating a Macaroon
```elixir
m = Macaroon.create_macaroon("http://my.cool.app", "public_id", "SUPER_SECRET_KEY_DO_NOT_SHARE")
```
### Adding Caveats
```elixir
m = Macaroon.create_macaroon("http://my.cool.app", "public_id", "SUPER_SECRET_KEY_DO_NOT_SHARE")
|> Macaroon.add_first_party_caveat("upload_limit = 4MB")
|> Macaroon.add_first_party_caveat("upload_namespace = /users/1234/*")
|> Macaroon.add_third_party_caveat("https://auth.another.app", "identity_caveat", "SECRET_SHARED_KEY")
```
### Verification
```elixir
alias Macaroon.Verification
result = Verification.satisfy_exact("upload_limit = 4MB")
|> Verification.satisfy_exact("upload_namespace = /users/1234/*")
|> Verification.satisfy_exact("time < 2022-01-01T00:00")
|> Verification.verify(macaroon, "SUPER_SECRET_KEY_DO_NOT_SHARE")
# result will be {:ok, macaroon} or {:error, reason_for_failure}
```
### Serialization and Deserialize
#### JSON
```elixir
{:ok, json_string} = Macaroon.create_macaroon("http://my.cool.app", "public_id", "SUPER_SECRET_KEY")
|> Macaroon.serialize(:json)
macaroon = Macaroon.deserialize(json_string, :json)
```
#### Binary
```elixir
{:ok, url_base64_string} = Macaroon.create_macaroon("http://my.cool.app", "public_id", "SUPER_SECRET_KEY")
|> Macaroon.serialize(:binary)
macaroon = Macaroon.deserialize(url_base64_string, :binary)
```
