Where to find logos

Facebook:

Easy to find, first google hit

Site      : https://www.facebookbrand.com/

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Google:

Medium hard to find

https://developers.google.com/+/api/openidconnect/

For Google SSO, it appears the Google+ logo should be used.??

Site:       https://developers.google.com/+/branding-guidelines
Download:   https://developers.google.com/+/images/branding/gplus-icons.zip


Or... 

Site:       https://developers.google.com/identity/branding-guidelines
Download:   https://developers.google.com/identity/images/signin-assets.zip


At the current stage, i appears the second should be used

API support : OpenID Connect
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Microsoft

Imposible to find, 
it's even hard to find where to register an app to use with SSO.
It's that I have a link on my site...
There it sends me to documentation "OneDrive API"
Even though I am not planning to use any storage, that seems the only
logo provided

Site:     https://msdn.microsoft.com/onedrive/dn673556
Download: http://go.microsoft.com/FwLink/p/?LinkID=390496

The Download link is located in-line text "this zipfile", not easy to find
when looking for a download

There is Microsoft sign in guidelines
https://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh968445.aspx
but that appears to be for Metro apps, not for sso usage
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LinkedIn

easy to find

Second Google hit: https://brand.linkedin.com/

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Twitter

Easy to find

https://about.twitter.com/press/brand-assets

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Yahoo

Login with openid buttons https://developer.yahoo.com/openid/loginbuttons.html
-- not suitable

To look at alter https://developer.yahoo.com/openid/
---
https://info.yahoo.com/press-center/logos-images : only wide logos... 
no square logo

http://www.findthatlogo.com/yahoo-logos/ <-- take one from there??

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Another possibility:

Logo pack http://www.flaticon.com/packs/simpleicon-social-media
--- so no official logos... but well... logos in one style... but if one is 
missing...
---

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Tumblr:

First google hit: https://www.tumblr.com/logo

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Vimeo:

First Google hit: https://vimeo.com/about/brand_guidelines

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VK:

Second google hit: http://vk.com/about

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WordPress:

First Google hit: https://wordpress.org/about/logos/

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Yandex:


Little clicking
http://company.yandex.com/general_info/logotype.xml

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Paypal:

first google
https://www.paypal.com/nl/webapps/mpp/logo-center

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Amazon

First google
http://phx.corporate-ir.net/phoenix.zhtml?c=176060&p=irol-logos

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Bitbucket

Little clicing
https://design.atlassian.com/2.0/how-we-design/resources/
-->
https://www.dropbox.com/sh/plg87rebd0jgxpm/AADSVrlULeUwPX245IBgJH5Ba?dl=0

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Bitly

little clicking around -- no square logo
https://bitly.com/pages/press

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Dropbox

fist hit https://www.dropbox.com/branding
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Etsy

Logo guidelines... but the logo itself?

ah... at press... again no square
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Flickr

ok, easy to find 
https://www.flickr.com/about/goodies/
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Github

First google https://github.com/logos
---
meetup


one click after first hit
http://help.meetup.com/customer/portal/articles/1802998-promotional-materials-for-your-meetup-group