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GitHub User: wbreeze
With Doorkeeper 0.7.4 I had to use callback = "urn:ietf:wg:oauth:2.0:oob" in place of the localhost:3001 callback. Otherwise, the page to exchange the authorization token for an accepted authorization code complained of a bad callback url.
callback = "urn:ietf:wg:oauth:2.0:oob"