Fix revoke access token error handling (#67)

- [x] Do not stop flow if revoke fails. 
- [x] Properly handle/log error

## Motivation and Context

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- [ ] My change requires a change to the documentation or CHANGELOG.
- [ ] I have updated the documentation/CHANGELOG accordingly.
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oauthproxy.go

@@ -815,16 +815,12 @@ func (p *OAuthProxy) backendLogout(rw http.ResponseWriter, req *http.Request, si
 		p.picsAuditClient.CreateSuccessfulLogoutAuditEntry(session, req.RequestURI, req.Header.Get("edisp-org-id"))
 	} else {
 		if providerData.BackendRevokeAccessTokenURL != "" {
-			resp, err := PicsRevokeAcessToken(providerData.BackendRevokeAccessTokenURL, session.AccessToken, providerData.ClientID, providerData.ClientSecret)
+			err := PicsRevokeAccessToken(providerData.BackendRevokeAccessTokenURL, session.AccessToken, providerData.ClientID, providerData.ClientSecret)
 			if err != nil {
 				logger.Errorf("error while calling backend revoke access token: %v", err)
-				return
+			} else {
+				p.picsAuditClient.CreateSuccessfulRevokeAccessTokenAuditEntry(session, req.RequestURI, req.Header.Get("edisp-org-id"))
 			}
-
-			if resp.StatusCode() != 200 {
-				logger.Errorf("error while calling backend revoke acess token url, returned error code %v", resp.StatusCode())
-			}
-			p.picsAuditClient.CreateSuccessfulRevokeAccessTokenAuditEntry(session, req.RequestURI, req.Header.Get("edisp-org-id"))
 		}
 
 		if providerData.BackendLogoutURL == "" {

pics_oauthproxy.go

@@ -35,11 +35,11 @@ func PicsSignOutAllSessions(backendLogoutAllSessionsURL string, introspectClaims
 	return resp, err
 }
 
-func PicsRevokeAcessToken(backendRevokeURL string, accessToken string, clientID string, clientSecret string) (resp requests.Result, err error) {
+func PicsRevokeAccessToken(backendRevokeURL string, accessToken string, clientID string, clientSecret string) (err error) {
 	authHeader := "Basic " + base64.StdEncoding.EncodeToString([]byte(clientID+":"+clientSecret))
 	body := "token=" + accessToken
 
-	resp = requests.New(backendRevokeURL).
+	resp := requests.New(backendRevokeURL).
 		WithMethod("POST").
 		SetHeader("Authorization", authHeader).
 		SetHeader("api-version", "2").
@@ -49,10 +49,14 @@ func PicsRevokeAcessToken(backendRevokeURL string, accessToken string, clientID
 		Do()
 
 	if resp.Error() != nil {
-		return nil, fmt.Errorf("error revoking access token: %v", resp.Error())
+		return fmt.Errorf("error revoking access token: %v", resp.Error())
 	}
 
-	return resp, nil
+	if resp.StatusCode() != 200 {
+		return fmt.Errorf("error revoking access token: status code %d, error: %v", resp.StatusCode(), resp.Error())
+	}
+
+	return nil
 }
 
 func getUserID(introspectClaims string) (string, error) {