Rename variable from args to query params for authz endpoint

[shawnhankim]

Issue:

• https://github.com/nginxinc/nginx-openid-connect/issues/77

Background:

• As a Product Manager, I want to more flexibly configure query parameters for the OIDC authZ endpoint. So customers can customize the OIDC endpoints to pass vendor specific query parameters to complete their flow. For example, Azure AD B2B expects to send a special query param called resource-id to be passed to its authorization endpoint.

In addition to that, I want to synchronize the variable name between NGINX Plus and NGINX Management Suite.

• NGINX Plus OIDC: $oidc_authz_extra_args is merged (Dec/8/2022)
• NGINX Management Suite: $oidc_authz_query_params is released (Jul/20/2022)

Description:

• Refactored and enhanced the existing reference implementation and the latest PR to support following options:
  • option 1. Use built-in params
  • option 2. Extend extra params after the built-in params
  • option 3. Replace built-in params with custom params
• Revised the name from $oidc_authz_extra_args to $oidc_authz_query_params.
• Added key/values (e.g., $pkce_code_challenge, $nonce_hash) that can be configured as query params by customers for the OIDC authZ endpoint.