[PECOBLR-15] Respect OAuth Discovery URL for ExternalBrowserCredentialsStrategy

[samikshya-db]

What changes are proposed in this pull request?

• WHAT : Discovery URL is currently being honored only in the M2M flow. This PR makes changes to honor it for U2M and other flows as well. Discovery URL was added by me last year in SDK for M2M flow Link
• I have also added a fallback to defaultOIDC flow to make this backward compatible too. skipped the fallback in this PR, will raise in a followup if I get approval from the SDK team
• WHY : A major customer ask is to extend discovery URL for U2M flow as well.

How is this tested?

Tested that discovery URL is being honored in U2M as well. Tested this using the OSS JDBC with the following URL

1. Success flow test :

String jdbcUrl =
        "jdbc:databricks://e2-dogfood.staging.cloud.databricks.com:443/default;transportMode=http;ssl=1;httpPath=/sql/1.0/warehouses/dd43ee29fedd958d;"
            + "AuthMech=11;Auth_Flow=2;LogLevel=6;UseThriftClient=0;EnableTokenCache=0;OIDCDiscoveryEndpoint=https://e2-dogfood.staging.cloud.databricks.com/oidc/.well-known/oauth-authorization-server";

2. Failure flow test :

String jdbcUrl =
        "jdbc:databricks://e2-dogfood.staging.cloud.databricks.com:443/default;transportMode=http;ssl=1;httpPath=/sql/1.0/warehouses/dd43ee29fedd958d;"
            + "AuthMech=11;Auth_Flow=2;LogLevel=6;UseThriftClient=0;EnableTokenCache=0;OIDCDiscoveryEndpoint=https://google.com";

[mgyucht]

For this PR, can we split out the fallback-to-default behavior to a separate discussion? Otherwise, the changes to the ExternalBrowserCredentialsStrategy and OAuthClient seem good to me.

[github-actions]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger:
go/deco-tests-run/sdk-java

Inputs:

• PR number: 505
• Commit SHA: a67b02a38ea76b0584dc36798071506f6db9708f

Checks will be approved automatically on success.

[mgyucht]

LGTM!