Swagger 2.0 or OpenAPI 3 definition challenge

I have an HTTP POST and Graph QL based authentication endpoint that takes the following parameters: 1. API_subscription_key (Header) 2. Content-Type: application/graphql (Header) 3. Query (QueryString), that looks like:

?query={getAccessToken(clientId: "abc",clientSecret: "xyz"){accessTokenFormat accessToken expiresOn}} 

I am building an API that uses Oauth 2 clientCredentials flow, to fetch the token from the above authentication endpoint and calls the subsequent APIs with the token to fetch data. How do I define the above securitySchemes using Open API 3 or Swagger 2.0? I tried defining like below but the swagger UI only shows Client ID, Client Secret text boxes and give an "Auth ErrorTypeError: Failed to fetch" when I input the client ID and client secret.

components:
  securitySchemes:
    myAPI_auth:    
      type: oauth2
      flows:
        clientCredentials:   
          tokenUrl: https://baseURL/graphql
          scopes:
            read_data: read the data