Fix 401 error in login route handler when login callback path is child of login path

[denysoblohin-okta]

Resolves https://github.com/okta/okta-oidc-js/issues/207

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Adding Tests
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation changes
• [ ] Other... Please describe:

What is the current behavior?

Issue Number: OKTA-262240

What is the new behavior?

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

Reviewers

[shuowu]

Can https://github.com/okta/okta-oidc-middleware/issues/20#issuecomment-528550857 be handled by this change?

[denysoblohin-okta]

@shuowu Can't reproduce error in #20 comment (and not sure about value of APP_ROOT for comment author, probably more info/code required about his project)

[shuowu]

Maybe try with a random root path, like /root. Or like what described in https://github.com/okta/okta-oidc-middleware/issues/20#issuecomment-551343166

[denysoblohin-okta]

Still can't reproduce with root path like described in https://github.com/okta/okta-oidc-middleware/issues/20#issuecomment-551343166