sequenceDiagram
    title Subscription Linking - Server-Side Systems Flow
    participant gis as GIS
    participant site as Publisher Site
    participant gcp as GCP
    participant pc as Publisher Center

    Note over site: client uses credentials.json 
 to sign api request
    site->>gis: signed request for access_token
    gis->>site: access_token returned
    Note over site: client uses access_token 
 to make api request
    site->>gcp: GET /publications/{publicationId}/readers/{ppid}
    gcp->>pc: Uses publicationId to validate 
 Subscription Linking config
    Note over pc: GCP projectId found in 
 Subscription Linking config
    pc->>gcp: GCP projectId returned
    Note over gcp: projectId used to 
 determine service account validity
    gcp->>site: readers/{ppid} returned