Hi!

Do we have a solouton for handling <link rel="alternative"> in DNN - other than manually adding this to the header on each page?

The alternative tells Google that, for example, 2 webpages actually are the same page. It could be the same page in to different languages or the same page for mobile phones and for desktops.

So there are 2 important occasions that this could be of great use for boosting your SEO.

1. When you have language support on your site.
https://support.google.com/webmasters/answer/189077

This should not be that much trouble getting automated in the header as DNN already keeps track of the corresponding page localizations/languages? 

2. When your use a sepparate mobile site, instead of making your main website responsive (Separate URLs).
https://developers.google.com/webmasters/mobile-sites/mobile-seo/overview/select-config
https://www.google.com/webmasters/tools/mobile-friendly/

This is a little bit more tricky to solve. The URLs could differ quite much between the desktop and mobile sites. I guess we will need some kind of option for manipulating the URL output here.

Is there some way to achieve this in DNN? Maybe there are some plugin that I've missed? :)

Yes, I have read those articles. But I am not sure if this is what I am looking for. :)

This seems to be redirects. I am looking for links (canonical/alternativ) in the header, for the search engine only. Not for the users. 

This is what I would like to achieve for a mobile site:

http://m.mysite.com/some-page - mobile site with this in the header:

<link rel="canonical" href="http://mysite.com/some-page" >

http://mysite.com/some-page - regular site with this in the header:

<link rel="alternate" media="only screen and (max-width: 640px)" href="http://m.mysite.com/some-page" >

One can add this manually. But that would be very time consuming if it needs to be done on a larger website.

This type of redirection could be very critical to pages that isn't responsive as this will start to affect Google ranking by 21 april.

http://googlewebmastercentral.blogspot.se/2015/02/finding-more-mobile-friendly-search.html 

The redirections for my multilanguage site works fine. I still can't see any tags like these though:

<link rel="alternate" href="http://mysite.com/en-us/some-url" hreflang="en-us" />