Apply openapi_prefix to redirect URL

[nunomen]

For my application I need to use Apache as a Reverse Proxy, like this:

<VirtualHost *:80>
    ServerName ${SERVER_NAME}
    DocumentRoot ${SERVER_DOCUMENT_ROOT}
    ##  Other Redirects
    
    ## FastApi App
    Redirect permanent /app    ${SERVER_NAME}:/app
</VirtualHost>

<VirtualHost *:443>
    ProxyPass         "/app" "http://localhost:57012"
    ProxyPassReverse  "/app" "http://localhost:57012"

In order to do this, I have to setup the fastapi app with the following settings:

app = FastAPI(
    title="app",
    description="Ipsum Lorem",
    openapi_prefix="/app",
    swagger_ui_init_oauth={"clientId": "app-id",},
)

The openapi_prefix is needed to set up the application behind a reverse proxy as carefully explained in FastApi documentation, otherwise openapi.json is not served in the right place. But, for some reason this openapi_prefix was not being applied on the oauth2 redirect_uri in the swagger html generator.

[nunomen]

Travis build was failing because of this:

fastapi/applications.py:116: error: Unsupported operand types for + ("str" and "None")
fastapi/applications.py:116: note: Right operand is of type "Optional[str]"

I don't really understand how these type checkers work, but it doesn't seem to me that Optional[str] is the appropriate choice, given that swagger_ui_oauth2_redirect_url is never None and has a default value of type str.

[nunomen]

Build is still failing and I'm trying to find what is wrong since the 3 first builds don't explicitly say which error was raised.

[codecov]

Codecov Report

Merging #1159 into master will not change coverage by %.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##            master     #1159     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files          331       223    -108     
  Lines         8085      6668   -1417     
===========================================
- Hits          8085      6668   -1417     

Impacted Files	Coverage Δ
fastapi/applications.py	100.00% <100.00%> (ø)
fastapi/utils.py	100.00% <0.00%> (ø)
fastapi/routing.py	100.00% <0.00%> (ø)
docs/src/app_testing/tutorial002.py
docs/src/security/tutorial005.py
docs/src/additional_responses/tutorial001.py
docs/src/dependencies/tutorial006.py
docs/src/custom_request_and_route/tutorial003.py
docs/src/sql_databases/sql_app/crud.py
docs/src/custom_request_and_route/tutorial002.py
... and 105 more

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[nunomen]

Duplicate of #1199

[tiangolo]

Thanks for your work @littlebrat ! Clever implementation. But yeah, with #1199 we can handle the issue from the "root" 😄