Correspond to AssumeRole and MFA

[goldeneggg]

Problem

lsec2 has not supported the AssumeRole and MFA.

Goal

Usage as follows. (See: Using an IAM Role in the AWS CLI - AWS Command Line Interface)

# set source profile and role profile into ~/.aws/config (use MFA)
[profile abc]
region=ap-northeast-1

[profile abc-role1]
region=ap-northeast-1
source_profile=abc
role_arn=arn:aws:iam::123456789012:role/HogeRole
mfa_serial=arn:aws:iam::987654321098:mfa/your.name

# set credential of source profile ~/.aws/credential
[abc]
aws_access_key_id = YOUR_ACCESS_KEY_ID
aws_secret_access_key = YOUR_SECRET_ACCESS_KEY

# Run lsec2 with `--profile ROLE_PROFILE_NAME` option
$ lsec2 --profile abc-role1 -H 
Assume Role MFA token code: [INPUT YOUR_MFA_TOKEN]

INSTANCE_ID     PRIVATE_IP      PUBLIC_IP       TYPE    STATE   TAGS
i-xxxxxxxxxx    172.456.789.000    UNDEFINED       t2.micro        stopped Name=sss
i-yyyyyyyyyy    172.456.789.000    10.11.12.13      t3.micro        running Name=ttt

Should we set AWS_SDK_LOAD_CONFIG env value?

No. We don't need to set AWS_SDK_LOAD_CONFIG env value.

What do I do NOT do in this PR?

I still don't support the MFA caching.

This feature had be discussed on aws/aws-sdk-go#1329, aws/aws-sdk-go#2375, kubernetes-sigs/aws-iam-authenticator#193 and others.

Workaround before merge this PR

1. Generate session token (using AWS STS)
2. Export envs with generated tokens
3. Run lsec2

$ aws sts assume-role --role-arn arn:aws:iam::YOURROLEID:role/YOURROLE --role-session-name RoleSession1 --serial-number arn:aws:iam::YOURUSERID:mfa/YOURACCOUNT --token-code MFA_DIGITS --profile YOURPROFILE

{
    "Credentials": {
        "AccessKeyId": "TMP_KEYID",
        "SecretAccessKey": "TMP_ACCESSKEY",
        "SessionToken": "TMP_SESSIONTOKEN",
        "Expiration": "2019-07-09T09:13:29Z"
    },
    "AssumedRoleUser": {
        "AssumedRoleId": "ROLEID:hoge",
        "Arn": "arn:aws:sts::222222222222:assumed-role/ROLENAME/hoge"
    }
}

$ export AWS_ACCESS_KEY_ID=TMP_KEYID
$ export AWS_SECRET_ACCESS_KEY=TMP_ACCESSKEY
$ export AWS_SESSION_TOKEN=TMP_SESSIONTOKEN

# Check your settings
$ lsec2

[codecov]

Codecov Report

Merging #21 into master will increase coverage by 0.24%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #21      +/-   ##
==========================================
+ Coverage   87.67%   87.91%   +0.24%     
==========================================
  Files           3        3              
  Lines         146      149       +3     
==========================================
+ Hits          128      131       +3     
  Misses         11       11              
  Partials        7        7