title: error : redirect_uri_mismatch :: The redirect_uri MUST match the registered callback URL
body: <p>So I am trying to learn OAuth in Flask using Github OAuth API and I am using <code>flask_dance</code> library for it. I am able to authenticate myself on Github and return back to my app but in its showing <code>404 Not Found Error</code> and in the url its <code>http://localhost:5000/login/authorized?error=redirect_uri_mismatch&amp;error_description=The+redirect_uri+MUST+match+the+registered+callback+URL+for+this+application...</code> , The callback url seems correct as it is what I gave on github but still its showing <code>redirect_uri mismatch</code> .
  I was reading the documentation <a href="https://developer.github.com/apps/managing-oauth-apps/troubleshooting-oauth-app-access-token-request-errors/#redirect-uri-mismatch" rel="nofollow noreferrer">here</a> and got to know that we can remove <code>redirect_uri</code> parameter from the request but I am not sure how to do that. 
  ( and I am on Windows 10 )<br>
  Any help would be nice. Thanks.</p>
  
  <p><a href="https://i.stack.imgur.com/GgDXa.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GgDXa.jpg" alt="shown here"></a></p>
  
  <h2>App.py</h2>
  
  <pre><code>from flask import Flask, redirect, url_for
  from werkzeug.contrib.fixers import ProxyFix
  from flask_dance.contrib.github import make_github_blueprint, github
  
  app = Flask(__name__)
  app.wsgi_app = ProxyFix(app.wsgi_app)
  app.secret_key = "supersekrit"
  blueprint = make_github_blueprint(
      client_id="xxxxxxxxx",
      client_secret="xxxxxxxx",
  )
  app.register_blueprint(blueprint, url_prefix="/login")
  
  @app.route("/signup")
  def index():
      if not github.authorized:
          return redirect(url_for("github.login"))
      resp = github.get("/user")
      assert resp.ok
      return "You are @{login} on GitHub".format(login=resp.json()["login"])
  
  if __name__ == "__main__":
      app.run(debug=True)
  </code></pre>