useGetAuthenticatedUser.tsx

/**
 * Fetch a CorpUser object corresponding to the currently authenticated user.
 */
export function useGetAuthenticatedUser(skip?: boolean) {
    const userUrn = Cookies.get(CLIENT_AUTH_COOKIE);
    if (!userUrn) {
        throw new Error('Could not find logged in user.');
    }
    const { data, error } = useGetMeQuery({ skip, fetchPolicy: 'cache-and-network' });
    if (error) {
        console.error(`Could not fetch logged in user from cache. + ${error.message}`);
    }
    return data?.me;
}

/**
 * Fetch an urn corresponding to the authenticated user.
 */
export function useGetAuthenticatedUserUrn() {
    const userUrn = Cookies.get(CLIENT_AUTH_COOKIE); // <---- This is the error
    if (!userUrn) {
        throw new Error('Could not find logged in user.'); 
    }
    return userUrn;
}

/**
 * Name of the auth cookie checked on client side (contains the currently authenticated user urn).
 */
export const CLIENT_AUTH_COOKIE = 'actor';

actor

actor = "urn:li:corpuser:my_email@address.com"

function get (name) {
    if (typeof document === 'undefined' || (arguments.length && !name)) {
      return
    }

    // To prevent the for loop in the first place assign an empty array
    // in case there are no cookies at all.
    var cookies = document.cookie ? document.cookie.split('; ') : []
    var jar = {}
    for (var i = 0; i < cookies.length; i++) {
      var parts = cookies[i].split('=')
      var value = parts.slice(1).join('=')

      try {
        var found = decodeURIComponent(parts[0])
        jar[found] = converter.read(value, found)

        if (name === found) {
          break
        }
      } catch (e) {}
    }

    return name ? jar[name] : jar
  }

var cookies = document.cookie ? document.cookie.split('; ') : []