!!! Overview 
[{$pagename}] is defined in [RFC 6415] and describes a [Discovery Mechanism] for [metadata] as well as information about individual [resources] controlled by the host.

[RFC 6415] document also registers the [well-known] [URI] suffix "[host-meta]" in the [Well-known] [URI] Registry established by [RFC 5785].

[{$pagename}]  registers the "lrdd" relation type in the [Link Relation Types] Registry

!! Obtaining [host-meta] Documents
The client obtains the [host-meta] document for a given host by sending an [HTTP] [RFC 2616] or an [HTTPS] [RFC 2818] [GET|HTTP GET] request to the host for the "/.well-known/host-meta" path, using the default ports defined for each [protocol] (e.g., port 80 for HTTP and port 443 for HTTPS). The scope and meaning of host-meta documents obtained via other protocols or ports is undefined.

The server [MUST] support at least one [protocol] but [MAY] support both. If both [protocols] are supported, they [MUST] produce the same document.

!! [{$pagename}] [Example]
For example, the following request is used to obtain the host-meta document for the 'example.com' host:
%%prettify 
{{{
GET /.well-known/host-meta HTTP/1.1
 Host: example.com
}}} /%
If the server response indicates that the [host-meta] resource is located elsewhere (a 301, 302, or 307 response status code), the client SHOULD try to obtain the resource from the location provided in the response.  This means that the host-meta document for one host [MAY] be retrieved from another host.  Likewise, if the resource is not available or does not exist (e.g., a 404 or 410 response status code), the client SHOULD infer that metadata is not available via this mechanism.

The [host-meta] document [SHOULD] be served with the "application/xrd+xml" media type and is in [XRD].

The client [MAY] request a [JRD] representation using the [HTTP] "Accept" request header field with a value of "application/json".  The server [MUST] include the [HTTP Response Header] "Content-Type" with a value of "application/json".  Any other "Content-Type" value (or lack thereof) indicates that the server does not support the [JRD] format.

Alternatively, the client MAY request a JRD representation by requesting the "host-meta.json" well-known document, by making a %%prettify 
{{{
GET /.well-known/host-meta.json HTTP/1.1
 Host: example.com
}}} /% 
following the same process used for "/.well-known/host-meta".  If the server does not support serving a JRD representation at this location, the server [MUST] respond with an HTTP 404 (Not Found) status code.

!! [Resource]-specific Information
In addition, there are times when a host-wide scope for policy or metadata is too coarse-grained. [{$pagename}] provides two mechanisms for providing resource-specific information:
* Link Templates - links using a URI template instead of a fixed target URI, providing a way to define generic rules for generating resource-specific links by applying the individual resource URI to the template.
* [Link-based Resource Descriptor Documents] ([LRDD]), pronounced 'lard') - descriptor documents providing resource-specific information, typically information that cannot be expressed using link templates. LRDD documents are linked to resources or host-meta documents using link templates with the "lrdd" relation type.

!! [{$pagename}] [Example]
Using [Google] Gmail [http://gmail.com/.well-known/host-meta|http://gmail.com/.well-known/host-meta|target='_blank'] obtains an [XML] [eXtensible Resource Descriptor Sequence] ([XRDS]) document:
%%prettify 
{{{
<?xml version='1.0' encoding='UTF-8'?>
<!-- NOTE: this host-meta end-point is a pre-alpha work in progress.   Don't rely on it. -->
<!-- Please follow the list at http://groups.google.com/group/webfinger -->
<XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0' 
     xmlns:hm='http://host-meta.net/xrd/1.0'>
  <hm:Host xmlns='http://host-meta.net/xrd/1.0'>gmail.com</hm:Host>
  <Link rel='lrdd' 
        template='https://profiles.google.com/_/webfinger/?q={uri}'>
    <Title>Resource Descriptor</Title>
  </Link>
</XRD>
}}} 
/%

! [OpenID Provider Issuer Discovery]
Using the provided "template [URL]" provided [http://www.google.com/s2/webfinger/?q=jwilleke@gmail.com|http://www.google.com/s2/webfinger/?q=jwilleke@gmail.com|target='_blank'] obtains an [XML] [XRDS] document:
%%prettify 
{{{
<?xml version='1.0'?>
<XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
	<Subject>acct:jwilleke@gmail.com</Subject>
	<Alias>http://www.google.com/profiles/jwilleke</Alias>
	<Link rel='http://portablecontacts.net/spec/1.0' href='http://www-opensocial.googleusercontent.com/api/people/'/>
	<Link rel='http://portablecontacts.net/spec/1.0#me' href='http://www-opensocial.googleusercontent.com/api/people/110925871223838855670/'/>
	<Link rel='http://webfinger.net/rel/profile-page' href='http://www.google.com/profiles/jwilleke' type='text/plain'/>
	<Link rel='http://microformats.org/profile/hcard' href='http://www.google.com/profiles/jwilleke' type='text/plain'/>
	<Link rel='http://gmpg.org/xfn/11' href='http://www.google.com/profiles/jwilleke' type='text/plain'/>
	<Link rel='http://specs.openid.net/auth/2.0/provider' href='http://www.google.com/profiles/jwilleke'/>
	<Link rel='describedby' href='http://www.google.com/profiles/jwilleke' type='text/plain'/>
	<Link rel='describedby' href='https://www.google.com/s2/webfinger/?q=jwilleke@gmail.com&amp;fmt=foaf' type='application/rdf+xml'/>
</XRD>
}}} 
/%
Which shows the [OpenID Connect Provider] url (http://specs.openid.net/auth/2.0/provider). 

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]