make origin_ssl_protocols configurable (#112)

## what
* This change allows you to configure the `origin_ssl_protocols` parameter
of the `aws_cloudfront_distribution` terraform resource. If this
parameter is not configured explicitly, the old default is kept.

## why
* This is just for making the module more flexible.

README.md

@@ -1,4 +1,6 @@
+<!-- markdownlint-disable -->
 # terraform-aws-cloudfront-s3-cdn [![Codefresh Build Status](https://g.codefresh.io/api/badges/pipeline/cloudposse/terraform-modules%2Fterraform-aws-cloudfront-s3-cdn?type=cf-1)](https://g.codefresh.io/public/accounts/cloudposse/pipelines/5d169121757962ff25679794) [![Latest Release](https://img.shields.io/github/release/cloudposse/terraform-aws-cloudfront-s3-cdn.svg)](https://travis-ci.org/cloudposse/terraform-aws-cloudfront-s3-cdn/releases) [![Slack Community](https://slack.cloudposse.com/badge.svg)](https://slack.cloudposse.com)
+<!-- markdownlint-restore -->
 
 [![README Header][readme_header_img]][readme_header_link]
 
@@ -201,6 +203,7 @@ Available targets:
 | origin\_bucket | Origin S3 bucket name | `string` | `""` | no |
 | origin\_force\_destroy | Delete all objects from the bucket so that the bucket can be destroyed without error (e.g. `true` or `false`) | `bool` | `false` | no |
 | origin\_path | An optional element that causes CloudFront to request your content from a directory in your Amazon S3 bucket or your custom origin. It must begin with a /. Do not add a / at the end of the path. | `string` | `""` | no |
+| origin\_ssl\_protocols | The SSL/TLS protocols that you want CloudFront to use when communicating with your origin over HTTPS. | `list(string)` | <pre>[<br>  "TLSv1",<br>  "TLSv1.1",<br>  "TLSv1.2"<br>]</pre> | no |
 | override\_origin\_bucket\_policy | When using an existing origin bucket (through var.origin\_bucket), setting this to 'false' will make it so the existing bucket policy will not be overriden | `bool` | `true` | no |
 | parent\_zone\_id | ID of the hosted zone to contain this record  (or specify `parent_zone_name`) | `string` | `""` | no |
 | parent\_zone\_name | Name of the hosted zone to contain this record (or specify `parent_zone_id`) | `string` | `""` | no |
@@ -383,8 +386,10 @@ Check out [our other projects][github], [follow us on twitter][twitter], [apply
 
 ### Contributors
 
+<!-- markdownlint-disable -->
 |  [![Erik Osterman][osterman_avatar]][osterman_homepage]<br/>[Erik Osterman][osterman_homepage] | [![Andriy Knysh][aknysh_avatar]][aknysh_homepage]<br/>[Andriy Knysh][aknysh_homepage] | [![Jamie Nelson][Jamie-BitFlight_avatar]][Jamie-BitFlight_homepage]<br/>[Jamie Nelson][Jamie-BitFlight_homepage] | [![Clive Zagno][cliveza_avatar]][cliveza_homepage]<br/>[Clive Zagno][cliveza_homepage] | [![David Mattia][dmattia_avatar]][dmattia_homepage]<br/>[David Mattia][dmattia_homepage] |
 |---|---|---|---|---|
+<!-- markdownlint-restore -->
 
   [osterman_homepage]: https://github.com/osterman
   [osterman_avatar]: https://img.cloudposse.com/150x150/https://github.com/osterman.png

docs/terraform.md

@@ -75,6 +75,7 @@
 | origin\_bucket | Origin S3 bucket name | `string` | `""` | no |
 | origin\_force\_destroy | Delete all objects from the bucket so that the bucket can be destroyed without error (e.g. `true` or `false`) | `bool` | `false` | no |
 | origin\_path | An optional element that causes CloudFront to request your content from a directory in your Amazon S3 bucket or your custom origin. It must begin with a /. Do not add a / at the end of the path. | `string` | `""` | no |
+| origin\_ssl\_protocols | The SSL/TLS protocols that you want CloudFront to use when communicating with your origin over HTTPS. | `list(string)` | <pre>[<br>  "TLSv1",<br>  "TLSv1.1",<br>  "TLSv1.2"<br>]</pre> | no |
 | override\_origin\_bucket\_policy | When using an existing origin bucket (through var.origin\_bucket), setting this to 'false' will make it so the existing bucket policy will not be overriden | `bool` | `true` | no |
 | parent\_zone\_id | ID of the hosted zone to contain this record  (or specify `parent_zone_name`) | `string` | `""` | no |
 | parent\_zone\_name | Name of the hosted zone to contain this record (or specify `parent_zone_id`) | `string` | `""` | no |

main.tf

@@ -218,7 +218,7 @@ resource "aws_cloudfront_distribution" "default" {
         http_port              = 80
         https_port             = 443
         origin_protocol_policy = "http-only"
-        origin_ssl_protocols   = ["TLSv1", "TLSv1.1", "TLSv1.2"]
+        origin_ssl_protocols   = var.origin_ssl_protocols
       }
     }
   }

variables.tf

@@ -417,3 +417,9 @@ variable "cloudfront_origin_access_identity_path" {
   default     = ""
   description = "Existing cloudfront origin access identity path used in the cloudfront distribution's s3_origin_config content"
 }
+
+variable "origin_ssl_protocols" {
+  type        = list(string)
+  default     = ["TLSv1", "TLSv1.1", "TLSv1.2"]
+  description = "The SSL/TLS protocols that you want CloudFront to use when communicating with your origin over HTTPS."
+}