isabella232 / aws_credentials

An Erlang library to provide AWS credentials

aws_credentials

This is a library to retrieve AWS credentials from a variety of possible sources in the following default order:

1. Erlang environment variables
2. OS environment variables
3. An AWS credentials file
4. ECS task credentials
5. EC2 metadata

Dependencies

This library depends on the following libraries:

• iso8601
• jsone
• eini

Implementation

Each possible location for credentials is an Erlang module which implements the aws_credentials_provider behaviour. The first provider to respond with (apparently) valid credentials stops evaluation of later providers.

Adding a new provider

If you want to add a new provider, you simply implement the behaviour and add the module name to the default list of modules to attempt.

Provider return values

Providers are expected to return either {error, Reason :: term()} or {ok, Credentials :: map(), Expiration :: infinity | binary() | pos_integer()}. The Credentials map typically looks like the following:

#{
  provider_source => Provider :: atom(),
  access_key_id => AccessKey :: binary(),
  secret_access_key => SecretKey :: binary(),
  token => Token :: binary(),
  region => Region :: binary()
}

Not all providers will populate all map keys.

The expiration time from a provider can either be expressed as:

• the atom infinity,
• epoch seconds as an integer, or,
• as an ISO8601 time/date string (e.g., "2019-03-14T23:45:56Z").

If you specify the expiration as infinity the library will never attempt to refresh credentials.

When credentials have been found, they will be cached in a gen_server until the credential's expiration time. 5 minutes before expiration time the gen_server will attempt to acquire new credentials, so credentials will automatically be refreshed in the background.

Usage

Include the library in your rebar.config file, and then...

{ok, _} = application:ensure_all_started(aws_credentials),
{ok, Credentials} = aws_credentials:get_credentials(),

By default if the library is unable to obtain credentials, it will fail to start with a bad_match exception, however if you set fail_if_unavailable to false then the library will ignore the exception and attempt to fetch credentials again after 5 seconds.

It is best practice to not cache these credentials inside of your own application. Always use the aws_credentials library to retrieve them - this way you will always get "fresh" credentials from the internal state of the application.

Choosing certain credentials providers

If you want to change the order of providers used to retrieve credentials, you can change the list of modules in your erlang environment variables as in this example:

  {aws_credentials, [{provider_list, [aws_credentials_ecs]}]
  },

Different credential providers may have other settings which you can use to change their behaviors. See the documentation for each provider for more details.

License and copyright

This project is licensed under the terms of the Apache 2 license. It is a heavily modified fork of the original aws-erlang-metadata project.

Copyright (C) 2018 by Mark R. Allen.