Description

when cloning the raw spec, the base_uri information is lost, meaning external references cannot be resolved.
maybe my use-case is niche, but my openapi spec relies heavily on external references

Expected behaviour

the spec to be displayed

Actual behaviour

500 error

Steps to reproduce

run the test in test_swagger_ui.py in #1889 with the modified simple app

Additional info:

Output of the commands:

• python --version
• pip show connexion | grep "^Version\:"