Include the "scheme" in self links

[bsnow-shl]

Rdap self links do not include the "scheme" - the protocol prefix like http:// or https:// - so they are neither valid relative nor absolute links (referred to as suffix references in rfc 3986). This PR adds the "scheme" and the "://" to each of the Servlets, as part of the variable called "header". The header goes nowhere other than the Link object, so this seems to work well and maintain consistency.

This change is RFC compliant, and brings reddog in line with verisign rdap, as well as all the usual REST services. The following is an example of a new links section:

  "links": [
    {
      "value": "https://example.com/entity/22-handle",
      "rel": "self",
      "href": "https://example.com/entity/22-handle",
      "type": "application/rdap+json"
    }
  ]

See also:
links section example includes scheme: https://tools.ietf.org/html/rfc7483#section-4.2
suffix references are discouraged: https://tools.ietf.org/html/rfc3986#section-4.5
verisign rdap example: https://rdap-pilot.verisignlabs.com/rdap/v1/entity/299~VRSN

[pcarana]

Thanks for contribute with this fix. Just as stated, the change is RFC compliant, so we will work on it to release it as soon as possible.

[pcarana]

In order to complete the proposal, the commit 5f251bb has been made to consider that the server can be behind a proxy/balancer.

Now the scheme will be retrieved considering HTTP headers "Forwarded" (optional and defined at RFC 7239 section 5.4) and "X-Forwarded-Proto" (a de facto standard); headers that could be sent by a proxy/balancer. If none of those headers is sent, then the function getScheme() is used to get the scheme.

[bsnow-shl]

This is a very thoughtful addition, and it continues to work with my code. I have been testing with registrobr/rdap-client

Thanks!

[pcarana]

Nice! Thanks for the help, now looking for the team's approval.

[pcarana]

Looks good, anything to add @dhfelix ? Also looking for review of @TheRedTrainer .

[TheRedTrainer]

Verified. The scheme is included in self links, even if the request is managed by a proxy server.

[brattienattie83]

Verified. The scheme is included in self links, even if the request is managed by a proxy server.

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