feat: reverse shares (#86)

* add first concept

* add reverse share funcionality to frontend

* allow creator to limit share expiration

* moved reverse share in seperate module

* add table to manage reverse shares

* delete complete share if reverse share was deleted

* optimize function names

* add db migration

* enable reverse share email notifications

* fix config variable descriptions

* fix migration for new installations

backend/src/share/guard/createShare.guard.ts

@@ -0,0 +1,29 @@
+import { ExecutionContext, Injectable } from "@nestjs/common";
+import { JwtGuard } from "src/auth/guard/jwt.guard";
+import { ConfigService } from "src/config/config.service";
+import { ReverseShareService } from "src/reverseShare/reverseShare.service";
+
+@Injectable()
+export class CreateShareGuard extends JwtGuard {
+  constructor(
+    configService: ConfigService,
+    private reverseShareService: ReverseShareService
+  ) {
+    super(configService);
+  }
+
+  async canActivate(context: ExecutionContext): Promise<boolean> {
+    if (await super.canActivate(context)) return true;
+
+    const reverseShareTokenId = context.switchToHttp().getRequest()
+      .cookies.reverse_share_token;
+
+    if (!reverseShareTokenId) return false;
+
+    const isReverseShareTokenValid = await this.reverseShareService.isValid(
+      reverseShareTokenId
+    );
+
+    return isReverseShareTokenValid;
+  }
+}