Provider Registration API

Create an API endpoint `/provider/register` within the `providerservice` module/microservice.

Requirements:
- Input: The API accepts `firstname`, `lastname`, `email`, `regtype`, `regtypename`, and `tin#`.
- Define a `RegisterRequest` file/class containing these fields.
- Each field must have appropriate validation annotations such as `@NotNull`, `@NotBlank`.
- The API should check if the provided `tin#` exists in the `phy` table of the `pnas` database.
- If `tin#` is present, generate a `regid` as a UUID.
- Save all the registration details including `regid` into the `auth` table of the `claims_portal_db`.
- Use two separate databases (`pnas` and `claims_portal_db`) within the same application.
- Do not implement exception handling inside this API or related files; all exceptions must be handled globally via the shared global exception handler.
- Incorporate the standardized API response format as detailed in the provided API response specification.

Steps:
1. Define a `RegisterRequest` DTO with the specified fields and validation annotations.
2. Implement a service method to query `pnas` database's `phy` table for the supplied `tin#`.
3. If `tin#` exists, generate a UUID `regid`.
4. Persist the registration data, including `regid`, into the `auth` table of `claims_portal_db`.
5. Return the `regid` in the API response using the standardized format.

Output Format:
- Provide the complete code for the API controller method, DTO class `RegisterRequest`, and necessary service logic.
- Show configuration or snippets that demonstrate use of two databases in one application.
- Include validation annotations explicitly.
- Exclude any local exception handling; highlight use of global exception handler.

Notes:
- Assume global exception handler and API response structure are supplied separately.
- Ensure transactional integrity when working with multiple databases if applicable.
- Use UUID generation standard library methods available.

Icon: CodeBracketIcon
Category: programming
Tags: [API Development, Validation, Multi-Database]