login_fingerprint.c:148:10: error: incompatible pointer types passing 'FILE *' (aka 'struct __sFILE *') to parameter of type 'const char *' [-Wincompatible-pointer-types]
  148 |                 printf(back, BI_SILENT "\n");
      |                        ^~~~

Index: login_fingerprint.c
--- login_fingerprint.c.orig
+++ login_fingerprint.c
@@ -145,7 +145,7 @@ main(int argc, char **argv)
 	}
 
 	if (strcmp(service, "challenge") == 0) {
-		printf(back, BI_SILENT "\n");
+		fprintf(back, BI_SILENT "\n");
 		exit(0);
 	}
 
