Multiple post categories – single permalink

I created a post which is assigned to multiple categories.

Eg: I have a post “My Post”, and I put it in “foo” and “bar” categories.
Now my article will have two permalinks, “/foo/my-post” and “/bar/my-post“.
Google calls this a duplicate, which it considers to be spam, hence this is not what I want.

How can I use multiple categories but have the same permalink?
I want this only for SEO.

My current permalink structure is /%category%/%post_id%-%postname%.html

If you are using category name in permalink for a post, it’s not a good practice, especially, if you have two or more categories per post.

Solutions:
Use canonical link tag for the post and add it to your prefered absolute URL. Google will rank only this one and it won’t be as duplicate content.