Allow oAuth2 clientSecret

[NiasSt90]

In your xml format description here there was an oauth2 block to configure a individuell oauth2/oidc configuration. But these configuration sections lacks the option to provide a clientId/clientSecret like in the following example.

<incomingServer type="imap">
      <hostname>imap.my-server.com</hostname>
      <port>993</port>
      <socketType>SSL</socketType>
      <username>%EMAILADDRESS%</username>
      <authentication>OAuth2</authentication>
      <authentication>password-cleartext</authentication>
      <oAuth2>
        <issuer>sso.my-keycloak.com/auth/realms/myRealm<issuer>
        <scope>imap<scope>
        <authURL>https://sso.my-keycloak.com/auth/realms/myRealm/protocol/openid-connect/auth</authURL>
        <tokenURL>https://sso.my-keycloak.com/auth/realms/myRealm/protocol/openid-connect/token</tokenURL>
        <clientId>MUA</clientId>
        <clientSecret>not-so-secret</clientSecret>
      <oAuth2>
    </incomingServer>

In my opinion is this easier than to try to create dynamically a client on the target IDP. (mentioned here)

[benbucksch]

I agree. There's already <clientID>, and I just added <clientSecret>.

FIXED