If I have authorization from a site to copy one of their articles and publish it on my site. What is the clean way of making sure I won't get penalized in my SEO efforts?
Is there a safe way to give full credit?
If you can, don't copy all the article
It's a bad idea to copy a full article from another website because you generate duplicate content issues between your site and the other one (even if the author of the article accepted the copy).
A good way would be to copy just two or three lines of the original article and add some unique and relevant text from you. You can for example give your opinion on the subject. It's a good technique to give SEO credit to your article.
Moreover, in general, when you copy lines of text from an article, you need to insert a link to it to be safe in SEO-wise.
If the article must be copied
If you need to copy the entire article, you can put the