OIDC audience claim was hardcoded as `rucio`

[maany]

Description

The OIDC audience claim was hardcoded as rucio in the code, making it inflexible for different Rucio deployments.

Current Behavior

• Audience value was hardcoded in oidc-providers.ts
• No validation of audience claims in received JWT tokens
• Could not be configured for different environments

Expected Behavior

• Audience claim should be configurable via environment variable
• Should validate JWT tokens contain the expected audience
• Should support different values for different Rucio instances (standard Rucio uses rucio, ATLAS uses atlas-rucio-oidc-client)

Impact

The hardcoded value prevented proper OIDC authentication configuration for deployments requiring different audience values.

Resolution

Fixed in PR #687