two issuers with the same IssuerURL cause fulcio identity error

[midnightercz]

Test case:

Having configuration like this:

OIDCIssuers:
  - ClientID: sigstore
    Issuer: 'https://issuer1...'  # simplified
    IssuerURL: 'https://issuer1...'  # simplified
    Type: kubernetes
  - ClientID: 'https://kubernetes.default.svc'
    Issuer: 'https://issuer1...'  # simplified
    IssuerURL: 'https://issuer1'  # simplified
    Type: kubernetes

and setting identity token to kubernetes sa with audience set to "sigstore"

Result

cause fulcio to fail with
getting Fulcio signer: getting key from Fulcio: retrieving cert: POST https://fulcio-server-trusted-artifact-signer.....p1.openshiftapps.com/api/v1/signingCert returned 400 Bad Request: "{"code":3,"message":"There was an error processing the identity token","details":[]}"

because it tries to match the token with second issuer.

Expected result

Either it shouldn't be allowed to have two issuers with the same URL or fulcio should not fail