Add IAM EC2 auth

lib/vault/api/auth.rb

@@ -186,6 +186,60 @@ def aws_ec2(role, pkcs7, nonce = nil)
       return secret
     end
 
+    # Authenticate via AWS IAM auth method by providing a AWS CredentialProvider (either ECS, AssumeRole, etc.)
+    # If authentication is successful, the resulting token will be stored on the client and used
+    # for future requests.
+    #
+    # @example
+    #   Vault.auth.aws_iam("dev-role-iam", Aws::AssumeRoleCredentials.new, "vault.example.com", "https://sts.us-east-2.amazonaws.com") #=> #<Vault::Secret lease_id="">
+    #
+    # @param [String] role
+    # @param [CredentialProvider] credentials_provider
+    #   https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/CredentialProvider.html
+    # @param [String] iam_auth_header_value optional
+    #   As of Jan 2018, Vault will accept ANY or NO header if none is configured by the Vault server admin
+    # @param [String] sts_endpoint optional
+    #   https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_enable-regions.html
+    # @return [Secret]
+    def aws_iam(role, credentials_provider, iam_auth_header_value = nil, sts_endpoint = 'https://sts.amazonaws.com')
+      require "aws-sigv4"
+      require "base64"
+
+      request_body   = 'Action=GetCallerIdentity&Version=2011-06-15'
+      request_method = 'POST'
+
+      vault_headers = {
+        'User-Agent' => Vault::Client::USER_AGENT,
+        'Content-Type' => 'application/x-www-form-urlencoded; charset=utf-8'
+      }
+
+      vault_headers['X-Vault-AWS-IAM-Server-ID'] = iam_auth_header_value if iam_auth_header_value
+
+      sig4_headers = Aws::Sigv4::Signer.new(
+        service: 'sts',
+        region: region_from_sts_endpoint(sts_endpoint),
+        credentials_provider: credentials_provider
+      ).sign_request(
+        http_method: request_method,
+        url: sts_endpoint,
+        headers: vault_headers,
+        body: request_body
+      ).headers
+
+      payload = {
+        role: role,
+        iam_http_request_method: request_method,
+        iam_request_url: Base64.strict_encode64(sts_endpoint),
+        iam_request_headers: Base64.strict_encode64(vault_headers.merge(sig4_headers).to_json),
+        iam_request_body: Base64.strict_encode64(request_body)
+      }
+
+      json = client.post('/v1/auth/aws/login', JSON.fast_generate(payload))
+      secret = Secret.decode(json)
+      client.token = secret.auth.client_token
+      return secret
+    end
+
     # Authenticate via a TLS authentication method. If authentication is
     # successful, the resulting token will be stored on the client and used
     # for future requests.
@@ -215,5 +269,21 @@ def tls(pem = nil, path = 'cert')
       client.token = secret.auth.client_token
       return secret
     end
+
+    private
+
+    # Parse an AWS region from a STS endpoint
+    # STS in the China (Beijing) region (cn-north-1) is sts.cn-north-1.amazonaws.com.cn
+    # Take care changing below regex with that edge case in mind
+    #
+    # @param [String] sts_endpoint
+    #   https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_enable-regions.html
+    #
+    # @return [String] aws region
+    def region_from_sts_endpoint(sts_endpoint)
+      valid_sts_endpoint = %r{https:\/\/sts\.?(.*).amazonaws.com}.match(sts_endpoint)
+      raise "Unable to parse STS endpoint #{sts_endpoint}" unless valid_sts_endpoint
+      valid_sts_endpoint[1].empty? ? 'us-east-1' : valid_sts_endpoint[1]
+    end
   end
 end

spec/integration/api/auth_spec.rb

@@ -1,4 +1,5 @@
 require "spec_helper"
+require "aws-sigv4"
 
 module Vault
   describe Auth do
@@ -211,5 +212,51 @@ module Vault
         }.to_not change { subject.token }
       end
     end
+
+    describe "#aws_iam", vault: "> 0.7.3" do
+      before(:context) do
+        vault_test_client.sys.enable_auth("aws", "aws", nil)
+        vault_test_client.post("/v1/auth/aws/config/client", JSON.fast_generate("iam_server_id_header_value" => "iam_header_canary"))
+      end
+
+      after(:context) do
+        vault_test_client.sys.disable_auth("aws")
+      end
+
+      let!(:old_token) { subject.token }
+      let(:credentials_provider) do
+        double(
+          credentials:
+            double(access_key_id: 'very', secret_access_key: 'secure', session_token: 'thing')
+        )
+      end
+      let(:secret) { double(auth: double(client_token: 'a great token')) }
+
+      after do
+        subject.token = old_token
+      end
+
+      it "does not authenticate if iam_server_id_header_value does not match" do
+        expect(::Aws::Sigv4::Signer).to(
+          receive(:new).with(
+            service: 'sts', region: 'cn-north-1', credentials_provider: credentials_provider
+          ).and_call_original
+        )
+        expect do
+          subject.auth.aws_iam('a_rolename', credentials_provider, 'mismatched_iam_header', 'https://sts.cn-north-1.amazonaws.com.cn') 
+        end.to raise_error(Vault::HTTPClientError, /expected iam_header_canary but got mismatched_iam_header/)
+      end
+
+      it "authenticates and saves the token on the client" do
+        expect(subject).to receive(:post).and_return 'huzzah!'
+        expect(Secret).to receive(:decode).and_return secret
+        expect(::Aws::Sigv4::Signer).to(
+          receive(:new).with(
+            service: 'sts', region: 'cn-north-1', credentials_provider: credentials_provider
+          ).and_call_original
+        )
+        subject.auth.aws_iam('a_rolename', credentials_provider, 'iam_header_canary', 'https://sts.cn-north-1.amazonaws.com.cn')
+      end
+    end
   end
 end

spec/unit/auth_spec.rb

@@ -0,0 +1,30 @@
+require "spec_helper"
+
+module Vault
+  describe Authenticate do
+    let(:auth) { Authenticate.new(client: nil) }
+    describe "#region_from_sts_endpoint" do
+      subject { auth.send(:region_from_sts_endpoint, sts_endpoint) }
+
+      context 'with a china endpoint' do
+        let(:sts_endpoint) { "https://sts.cn-north-1.amazonaws.com.cn" }
+        it { is_expected.to eq 'cn-north-1' }
+      end
+
+      context 'with a GovCloud endpoint' do
+        let(:sts_endpoint) { "https://sts.us-gov-west-1.amazonaws.com" }
+        it { is_expected.to eq 'us-gov-west-1' }
+      end
+
+      context 'with no regional endpoint' do
+        let(:sts_endpoint) { "https://sts.amazonaws.com" }
+        it { is_expected.to eq 'us-east-1' }
+      end
+
+      context 'with a malformed url' do
+        let(:sts_endpoint) { "https:sts.amazonaws.com" }
+        it { expect { subject }.to raise_exception(StandardError, "Unable to parse STS endpoint https:sts.amazonaws.com") }
+      end
+    end
+  end
+end

vault.gemspec

@@ -19,6 +19,8 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
+  spec.add_runtime_dependency "aws-sigv4"
+
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "pry"
   spec.add_development_dependency "rake",    "~> 12.0"